docs: updated docs

Purchase flow: name -> placeholder -> configure via the shipped PlanConfigurator
-> Paddle overlay with custom_data -> paste install UUID to link and issue.
lineItemsFor mirrors the Go catalogue.LineItems/billable exactly (base included
in exactly one place). ManageBillingButton opens the hosted portal. Paddle token
and env are baked into the build, never fetched.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.gitea/workflows/server-deploy.yml

@@ -147,6 +147,8 @@ jobs:
                   docker build \
                     --build-arg NEXT_PUBLIC_ADMIN_API_URL="${{ vars.ADMIN_API_URL }}" \
                     --build-arg NEXT_PUBLIC_ADMIN_ENV="${{ vars.ADMIN_ENV }}" \
+                    --build-arg NEXT_PUBLIC_PADDLE_CLIENT_TOKEN="${{ vars.PADDLE_CLIENT_TOKEN }}" \
+                    --build-arg NEXT_PUBLIC_PADDLE_ENV="${{ vars.PADDLE_ENV }}" \
                     -t "$IMAGE" \
                     -f adminsite/Dockerfile adminsite/
                   docker push "$IMAGE"

admin/cmd/main.go

@@ -21,6 +21,7 @@ import (
 	"github.com/mrhid6/vantage/admin/internal/lifecycle"
 	"github.com/mrhid6/vantage/admin/internal/mail"
 	"github.com/mrhid6/vantage/admin/internal/models"
+	"github.com/mrhid6/vantage/admin/internal/paddle"
 )
 
 func main() {
@@ -34,6 +35,10 @@ func main() {
 	licensing.SetSigningKey(cfg.SigningKey)
 	api.SetAppLoginURL(cfg.AppLoginURL)
 
+	if _, err := paddle.Init(cfg.PaddleAPIKey, cfg.PaddleEnv); err != nil {
+		log.Fatalf("paddle init: %v", err)
+	}
+
 	mail.Init(mail.Config{
 		Host: cfg.SMTPHost, Port: cfg.SMTPPort, From: cfg.SMTPFrom,
 		Username: cfg.SMTPUsername, Password: cfg.SMTPPassword,

admin/internal/api/checkout.go

@@ -0,0 +1,256 @@
+package api
+
+import (
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
+	"github.com/mrhid6/vantage/admin/internal/audit"
+	"github.com/mrhid6/vantage/admin/internal/auth"
+	"github.com/mrhid6/vantage/admin/internal/billing"
+	"github.com/mrhid6/vantage/admin/internal/catalogue"
+	"github.com/mrhid6/vantage/admin/internal/db"
+	"github.com/mrhid6/vantage/admin/internal/models"
+	"github.com/mrhid6/vantage/admin/internal/paddle"
+	"github.com/mrhid6/vantage/shared/license"
+	"go.mongodb.org/mongo-driver/v2/bson"
+)
+
+// checkoutOptions serves everything the browser configurator needs to price a
+// plan: the active plans (base allowances), the full catalogue (component prices
+// in the running environment), and the environment name so the client can refuse
+// a mismatch. The client token itself is baked into the adminsite build, never
+// served from here.
+func checkoutOptions(c *gin.Context) {
+	ctx := c.Request.Context()
+	plans := []models.Plan{}
+	if cur, err := db.Admin("plans").Find(ctx, bson.M{"active": true}); err == nil {
+		_ = cur.All(ctx, &plans)
+	}
+	rows, err := models.AllCatalogue(ctx)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{
+		"plans":     plans,
+		"catalogue": rows,
+		"env":       paddle.Get().Env(),
+	})
+}
+
+// createSelfHostedPlaceholder makes an instance row that exists only so a
+// checkout has something to put in custom_data. It carries no licence and is
+// flagged Placeholder until the customer pastes their install's real UUID. The
+// generated id is temporary; linking replaces the identity.
+func createSelfHostedPlaceholder(c *gin.Context) {
+	s := auth.Current(c)
+	var body struct {
+		Name string `json:"name"`
+	}
+	if err := c.ShouldBindJSON(&body); err != nil || body.Name == "" {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "a name is required"})
+		return
+	}
+	ctx := c.Request.Context()
+	inst := models.Instance{
+		InstanceID:  uuid.NewString(),
+		AccountID:   s.AccountID,
+		Name:        body.Name,
+		Deployment:  license.DeploymentSelfHosted,
+		Status:      models.StatusAwaitingLink,
+		Placeholder: true,
+		CreatedAt:   time.Now().UTC(),
+	}
+	if _, err := db.Admin("admin_instances").InsertOne(ctx, inst); err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+	audit.Write(ctx, models.AuditEntry{
+		Actor: s.Email, Action: "instance.placeholder_created", AccountID: s.AccountID,
+		Target: inst.InstanceID, IP: c.ClientIP()})
+	c.JSON(http.StatusCreated, gin.H{"instance_id": inst.InstanceID})
+}
+
+// updateEntitlement sets an instance's DESIRED configuration and pushes the
+// resulting line items to Paddle. It does NOT issue — the resulting
+// subscription.updated webhook does, from granted. An increase is prorated
+// immediately by Paddle; a reduction is recorded as desired and takes effect at
+// renewal, so this never shrinks a live licence.
+func updateEntitlement(c *gin.Context) {
+	inst, ok := ownedInstance(c, c.Param("id"))
+	if !ok {
+		return
+	}
+	ctx := c.Request.Context()
+	var body struct {
+		Tier     string   `json:"tier"`
+		Term     string   `json:"term"`
+		Servers  int      `json:"servers"`
+		Features []string `json:"features"`
+	}
+	if err := c.ShouldBindJSON(&body); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid configuration"})
+		return
+	}
+
+	plan, err := models.GetPlan(ctx, inst.Deployment, body.Tier)
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "no such plan"})
+		return
+	}
+	if body.Servers < plan.BaseLimits.MaxServers && plan.BaseLimits.MaxServers != license.Unlimited {
+		c.JSON(http.StatusBadRequest, gin.H{
+			"error": fmt.Sprintf("%s includes %d servers", plan.Name, plan.BaseLimits.MaxServers)})
+		return
+	}
+
+	desired := models.Config{Servers: body.Servers, Features: models.Features(body.Features).OrEmpty()}
+	items, err := catalogue.LineItems(ctx, paddle.Get().Env(), body.Term, plan, desired)
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
+
+	// A live subscription is required to update. None means this instance has
+	// never been paid for — that is a checkout, not an update.
+	var sub models.Subscription
+	if err := db.Admin("subscriptions").FindOne(ctx,
+		bson.M{"instance_id": inst.InstanceID, "status": models.SubActive}).Decode(&sub); err != nil {
+		c.JSON(http.StatusConflict, gin.H{"error": "no active subscription; start a checkout instead"})
+		return
+	}
+
+	pItems := make([]paddle.LineItem, 0, len(items))
+	for _, it := range items {
+		pItems = append(pItems, paddle.LineItem{PriceID: it.PriceID, Quantity: it.Quantity})
+	}
+	if err := paddle.Get().UpdateSubscriptionItems(ctx, sub.PaddleSubscriptionID, pItems); err != nil {
+		c.JSON(http.StatusBadGateway, gin.H{"error": "billing update failed; nothing changed"})
+		return
+	}
+
+	// Record desired now; the webhook Paddle sends back promotes to granted and
+	// reissues. Recording here makes the portal reflect the intent instantly
+	// rather than waiting on the round-trip.
+	limits, _, _ := catalogue.Resolve(ctx, plan, desired)
+	next := models.Entitlement{
+		InstanceID: inst.InstanceID, AccountID: inst.AccountID,
+		Deployment: inst.Deployment, Tier: body.Tier, Term: body.Term,
+		Desired: desired, ResolvedLimits: limits,
+	}
+	ent, _ := models.GetEntitlement(ctx, inst.InstanceID)
+	if ent != nil {
+		next.Granted = ent.Granted
+		next.GrantedAt = ent.GrantedAt
+		if desired.Servers < ent.Granted.Servers {
+			now := time.Now().UTC()
+			next.ScheduledChangeAt = &now
+		}
+	} else {
+		next.Granted = desired
+	}
+	if err := models.UpsertEntitlement(ctx, next); err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+	audit.Write(ctx, models.AuditEntry{
+		Actor: auth.Current(c).Email, Action: "entitlement.requested",
+		AccountID: inst.AccountID, Target: inst.InstanceID})
+	c.JSON(http.StatusOK, gin.H{"entitlement": next, "pending": next.Pending()})
+}
+
+// claimPlaceholderLink binds a paid self-hosted placeholder to the customer's
+// real install UUID, then issues.
+//
+// :id is the placeholder (generated at checkout, carried in the subscription's
+// custom_data); the body carries the UUID the install actually reports. The
+// licence must bind to that real UUID (spec 1 has no unbound licence), so the
+// placeholder row's identity is rewritten to it and the subscription re-pointed,
+// then billing issues from the recorded subscription. Linking and claiming stay
+// one call here because, unlike Free, the payment already happened.
+func claimPlaceholderLink(c *gin.Context) {
+	inst, ok := ownedInstance(c, c.Param("id"))
+	if !ok {
+		return
+	}
+	if !inst.Placeholder {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "this instance is already linked"})
+		return
+	}
+	var body struct {
+		InstanceID string `json:"instance_id"`
+	}
+	if err := c.ShouldBindJSON(&body); err != nil || body.InstanceID == "" {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "instance_id is required"})
+		return
+	}
+	ctx := c.Request.Context()
+
+	// The real UUID must be free across every account — the unique index on
+	// instance_id is the tenant-isolation property, so refuse rather than collide.
+	if n, _ := db.Admin("admin_instances").CountDocuments(ctx,
+		bson.M{"instance_id": body.InstanceID}); n > 0 {
+		c.JSON(http.StatusConflict, gin.H{"error": "that instance ID is already linked"})
+		return
+	}
+
+	placeholderID := inst.InstanceID
+	if _, err := db.Admin("admin_instances").UpdateOne(ctx,
+		bson.M{"instance_id": placeholderID},
+		bson.M{"$set": bson.M{
+			"instance_id": body.InstanceID,
+			"status":      models.StatusActive,
+			"placeholder": false,
+		}}); err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+	// Re-point the subscription from the placeholder id to the real UUID so
+	// billing.IssueForInstance (and every later webhook) finds it.
+	if _, err := db.Admin("subscriptions").UpdateMany(ctx,
+		bson.M{"instance_id": placeholderID},
+		bson.M{"$set": bson.M{"instance_id": body.InstanceID}}); err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+
+	if err := billing.IssueForInstance(ctx, body.InstanceID); err != nil {
+		// The link stuck; issuance did not. The reconciler and a retry recover it,
+		// and the customer is not blocked from linking. Surface it, do not roll back.
+		c.JSON(http.StatusAccepted, gin.H{
+			"instance_id": body.InstanceID,
+			"warning":     "linked, but licence issuance is pending: " + err.Error()})
+		return
+	}
+	audit.Write(ctx, models.AuditEntry{
+		Actor: auth.Current(c).Email, Action: "instance.placeholder_linked",
+		AccountID: inst.AccountID, Target: body.InstanceID,
+		Detail: "from placeholder " + placeholderID, IP: c.ClientIP()})
+	c.JSON(http.StatusOK, gin.H{"instance_id": body.InstanceID})
+}
+
+// billingPortal mints a Paddle customer-portal URL. The account must already
+// have a paddle_customer_id, which it learns from its first subscription webhook.
+func billingPortal(c *gin.Context) {
+	s := auth.Current(c)
+	ctx := c.Request.Context()
+	var acc models.Account
+	if err := db.Admin("accounts").FindOne(ctx,
+		bson.M{"account_id": s.AccountID}).Decode(&acc); err != nil {
+		c.JSON(http.StatusNotFound, gin.H{"error": "no account"})
+		return
+	}
+	if acc.PaddleCustomerID == "" {
+		c.JSON(http.StatusConflict, gin.H{"error": "no billing account yet; buy a paid plan first"})
+		return
+	}
+	url, err := paddle.Get().PortalSession(ctx, acc.PaddleCustomerID)
+	if err != nil {
+		c.JSON(http.StatusBadGateway, gin.H{"error": "could not open billing portal"})
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{"url": url})
+}

admin/internal/api/paddle.go

@@ -0,0 +1,64 @@
+package api
+
+import (
+	"encoding/json"
+	"io"
+	"log"
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	"github.com/mrhid6/vantage/admin/internal/billing"
+	"github.com/mrhid6/vantage/admin/internal/config"
+	"github.com/mrhid6/vantage/admin/internal/models"
+	"github.com/mrhid6/vantage/admin/internal/paddle"
+)
+
+// paddleWebhook is the ingress for every Paddle event.
+//
+// Order is load-bearing: read the RAW body first (the signature is over the
+// exact bytes), verify, THEN claim the event ID, THEN dispatch. A bad signature
+// is 401 and processes nothing; a duplicate of a handled event is 200 and does
+// nothing; a handler error is 500 so Paddle retries, and is recorded for staff.
+func paddleWebhook(cfg config.Config) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		body, err := io.ReadAll(c.Request.Body)
+		if err != nil {
+			c.JSON(http.StatusBadRequest, gin.H{"error": "unreadable body"})
+			return
+		}
+		if !paddle.VerifySignature(cfg.PaddleWebhookSecret,
+			c.GetHeader("Paddle-Signature"), body) {
+			log.Printf("paddle webhook: bad signature from %s", c.ClientIP())
+			c.JSON(http.StatusUnauthorized, gin.H{"error": "bad signature"})
+			return
+		}
+
+		var ev billing.Event
+		if err := json.Unmarshal(body, &ev); err != nil || ev.EventID == "" {
+			c.JSON(http.StatusBadRequest, gin.H{"error": "malformed event"})
+			return
+		}
+
+		ctx := c.Request.Context()
+		claimed, err := models.ClaimEvent(ctx, ev.EventID, ev.EventType)
+		if err != nil {
+			c.JSON(http.StatusInternalServerError, gin.H{"error": "claim failed"})
+			return
+		}
+		if !claimed {
+			// Already handled (or in flight). 200 so Paddle stops retrying.
+			c.JSON(http.StatusOK, gin.H{"duplicate": true})
+			return
+		}
+
+		if err := billing.Dispatch(ctx, ev); err != nil {
+			log.Printf("paddle webhook: handler %s failed for %s: %v",
+				ev.EventType, ev.EventID, err)
+			_ = models.MarkEventProcessed(ctx, ev.EventID, err)
+			c.JSON(http.StatusInternalServerError, gin.H{"error": "handler failed"})
+			return
+		}
+		_ = models.MarkEventProcessed(ctx, ev.EventID, nil)
+		c.JSON(http.StatusOK, gin.H{"ok": true})
+	}
+}

admin/internal/api/routes.go

@@ -39,6 +39,10 @@ func Routes(cfg config.Config) http.Handler {
 	r.POST("/auth/signup", auth.HandleSignup)
 	r.POST("/auth/accept-invite", auth.HandleAcceptInvite)
 
+	// Public: Paddle carries no session cookie; its signature is its auth. Must
+	// NOT sit under the cust group's session middleware.
+	r.POST("/api/paddle/webhook", paddleWebhook(cfg))
+
 	cust := r.Group("/api")
 	cust.Use(auth.RequireCustomer())
 	{
@@ -72,6 +76,17 @@ func Routes(cfg config.Config) http.Handler {
 			auth.RequireAccountRole(models.AccountRoleOwner, models.AccountRoleAdmin),
 			claimFree)
 		cust.GET("/instances/:id/entitlement", getEntitlement)
+		cust.GET("/checkout/options", checkoutOptions)
+		cust.POST("/instances/self-hosted",
+			auth.RequireAccountRole(models.AccountRoleOwner, models.AccountRoleAdmin),
+			createSelfHostedPlaceholder)
+		cust.PUT("/instances/:id/entitlement",
+			auth.RequireAccountRole(models.AccountRoleOwner, models.AccountRoleAdmin),
+			updateEntitlement)
+		cust.POST("/billing/portal", billingPortal)
+		cust.POST("/instances/:id/claim-link",
+			auth.RequireAccountRole(models.AccountRoleOwner, models.AccountRoleAdmin),
+			claimPlaceholderLink)
 		cust.GET("/instances/:id/license", getInstanceLicense)
 		cust.GET("/instances/:id/license/download", downloadInstanceLicense)
 		cust.GET("/instances/:id/members", listInstanceMembers)
@@ -113,6 +128,7 @@ func Routes(cfg config.Config) http.Handler {
 		staff.PUT("/instances/:id/entitlement", staffSetEntitlement)
 		staff.GET("/audit", staffAudit)
 		staff.GET("/health/injection", staffInjectionHealth)
+		staff.GET("/health/billing", staffBillingHealth)
 	}
 
 	return r

admin/internal/api/staff.go

@@ -380,6 +380,29 @@ func staffListLicenses(c *gin.Context) {
 	c.JSON(http.StatusOK, lics)
 }
 
+// staffBillingHealth surfaces webhook handlers that failed and paid-but-unlinked
+// placeholders, so a customer who paid and got nothing is visible rather than
+// stuck in a support queue.
+func staffBillingHealth(c *gin.Context) {
+	ctx := c.Request.Context()
+	failed := []models.PaddleEvent{}
+	if cur, err := db.Admin("paddle_events").Find(ctx,
+		bson.M{"processed_at": bson.M{"$exists": false}, "error": bson.M{"$ne": ""}}); err == nil {
+		_ = cur.All(ctx, &failed)
+	}
+	unlinked := []models.Instance{}
+	if cur, err := db.Admin("admin_instances").Find(ctx,
+		bson.M{"placeholder": true, "status": models.StatusAwaitingLink}); err == nil {
+		_ = cur.All(ctx, &unlinked)
+	}
+	c.JSON(http.StatusOK, gin.H{
+		"failed_events":   failed,
+		"failed_count":    len(failed),
+		"unlinked_paid":   unlinked,
+		"unlinked_count":  len(unlinked),
+	})
+}
+
 func staffListPlans(c *gin.Context) {
 	cur, err := db.Admin("plans").Find(c.Request.Context(), bson.M{})
 	if err != nil {

admin/internal/billing/deliver.go

@@ -0,0 +1,24 @@
+package billing
+
+import (
+	"context"
+
+	"github.com/mrhid6/vantage/admin/internal/inject"
+	"github.com/mrhid6/vantage/admin/internal/mail"
+	"github.com/mrhid6/vantage/admin/internal/models"
+	"github.com/mrhid6/vantage/shared/license"
+)
+
+// deliver sends a freshly issued licence where it belongs. Cloud is injected;
+// self-hosted is emailed the blob (their database is theirs). This mirrors the
+// api-side deliver helper but takes no gin context — webhooks have none, and the
+// customer is not on the other end of the request.
+func deliver(ctx context.Context, inst *models.Instance, lic *models.License, to string) {
+	if inst.Deployment == license.DeploymentCloud {
+		inject.Deliver(ctx, lic)
+		return
+	}
+	if to != "" && mail.Enabled() {
+		_ = mail.SendLicense(to, inst.Name, lic.Blob)
+	}
+}

admin/internal/billing/events.go

@@ -0,0 +1,51 @@
+// Package billing turns verified Paddle webhooks into licence actions. It never
+// verifies signatures (that is paddle.VerifySignature at the edge) and never
+// signs (that is licensing.Issue); it decides what a subscription's current
+// state means and calls the issuer.
+package billing
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"time"
+)
+
+// Event is the decoded Paddle webhook envelope. Data is left raw so each handler
+// decodes only the shape it needs.
+type Event struct {
+	EventID    string          `json:"event_id"`
+	EventType  string          `json:"event_type"`
+	OccurredAt time.Time       `json:"occurred_at"`
+	Data       json.RawMessage `json:"data"`
+}
+
+// Dispatch routes one event to its handler. Unknown event types are a no-op
+// success: Paddle sends many we do not care about, and 200 stops it retrying.
+func Dispatch(ctx context.Context, ev Event) error {
+	switch ev.EventType {
+	case "subscription.created", "subscription.updated", "subscription.activated":
+		return handleSubscription(ctx, ev)
+	case "subscription.canceled":
+		return handleCanceled(ctx, ev)
+	case "subscription.past_due":
+		return handlePastDue(ctx, ev)
+	case "transaction.completed":
+		return handleTransactionCompleted(ctx, ev)
+	case "transaction.payment_failed":
+		return handlePaymentFailed(ctx, ev)
+	case "customer.updated":
+		return handleCustomerUpdated(ctx, ev)
+	default:
+		return nil
+	}
+}
+
+// decode is a small helper so every handler decodes Data the same way.
+func decode[T any](ev Event) (T, error) {
+	var v T
+	if err := json.Unmarshal(ev.Data, &v); err != nil {
+		return v, fmt.Errorf("decode %s: %w", ev.EventType, err)
+	}
+	return v, nil
+}

admin/internal/billing/subscription.go

@@ -0,0 +1,276 @@
+package billing
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"github.com/google/uuid"
+	"github.com/mrhid6/vantage/admin/internal/catalogue"
+	"github.com/mrhid6/vantage/admin/internal/db"
+	"github.com/mrhid6/vantage/admin/internal/licensing"
+	"github.com/mrhid6/vantage/admin/internal/mail"
+	"github.com/mrhid6/vantage/admin/internal/models"
+	"github.com/mrhid6/vantage/admin/internal/paddle"
+	"go.mongodb.org/mongo-driver/v2/bson"
+	"go.mongodb.org/mongo-driver/v2/mongo/options"
+)
+
+// subscriptionData is the slice of Paddle's subscription payload we read. Fields
+// we ignore are simply absent — encoding/json drops them.
+type subscriptionData struct {
+	ID         string `json:"id"`
+	CustomerID string `json:"customer_id"`
+	Status     string `json:"status"`
+	CustomData struct {
+		AccountID  string `json:"account_id"`
+		InstanceID string `json:"instance_id"`
+	} `json:"custom_data"`
+	CurrentBillingPeriod struct {
+		EndsAt time.Time `json:"ends_at"`
+	} `json:"current_billing_period"`
+	Items []struct {
+		Price struct {
+			ID string `json:"id"`
+		} `json:"price"`
+		Quantity int `json:"quantity"`
+	} `json:"items"`
+}
+
+func (d subscriptionData) lineItems() []catalogue.Item {
+	items := make([]catalogue.Item, 0, len(d.Items))
+	for _, it := range d.Items {
+		items = append(items, catalogue.Item{PriceID: it.Price.ID, Quantity: it.Quantity})
+	}
+	return items
+}
+
+// handleSubscription folds created/updated/activated into one job: make the
+// world match the subscription's CURRENT state. That is what keeps out-of-order
+// delivery correct — an updated arriving before its created still carries the
+// full item list, so reading all of it is reading current state, not a
+// transition.
+func handleSubscription(ctx context.Context, ev Event) error {
+	d, err := decode[subscriptionData](ev)
+	if err != nil {
+		return err
+	}
+	if d.CustomData.InstanceID == "" {
+		return fmt.Errorf("subscription %s has no instance_id in custom_data", d.ID)
+	}
+
+	match, err := catalogue.ResolveItems(ctx, paddle.Get().Env(), d.lineItems())
+	if err != nil {
+		// A price we cannot map is a configuration error, not a customer error.
+		// Fail loudly so it is retried and surfaced rather than guessed.
+		return fmt.Errorf("resolve items for subscription %s: %w", d.ID, err)
+	}
+
+	sub := models.Subscription{
+		AccountID:            d.CustomData.AccountID,
+		InstanceID:           d.CustomData.InstanceID,
+		PaddleSubscriptionID: d.ID,
+		Tier:                 match.Tier,
+		Term:                 match.Term,
+		Status:               d.Status,
+		CurrentPeriodEnd:     d.CurrentBillingPeriod.EndsAt,
+		Items:                toSubItems(d.lineItems()),
+	}
+	if err := upsertSubscription(ctx, sub); err != nil {
+		return err
+	}
+
+	// Learn the Paddle customer ID onto the account the first time we see it.
+	if d.CustomerID != "" && d.CustomData.AccountID != "" {
+		_, _ = db.Admin("accounts").UpdateOne(ctx,
+			bson.M{"account_id": d.CustomData.AccountID, "paddle_customer_id": bson.M{"$in": bson.A{nil, ""}}},
+			bson.M{"$set": bson.M{"paddle_customer_id": d.CustomerID}})
+	}
+
+	// A self-hosted placeholder that has not been linked yet gets its
+	// subscription recorded but NO licence — there is no UUID to bind to. The
+	// link endpoint issues when the customer pastes it.
+	var inst models.Instance
+	if err := db.Admin("admin_instances").FindOne(ctx,
+		bson.M{"instance_id": d.CustomData.InstanceID}).Decode(&inst); err != nil {
+		return fmt.Errorf("subscription %s names unknown instance %s: %w",
+			d.ID, d.CustomData.InstanceID, err)
+	}
+	if inst.Placeholder {
+		return nil
+	}
+
+	return promoteAndIssue(ctx, &inst, match, models.ReasonEntitlementChange)
+}
+
+// promoteAndIssue promotes desired→granted from the resolved match, then signs a
+// licence from granted. This is the only promotion path other than the staff
+// grant, and it exists because a webhook is a confirmed payment.
+func promoteAndIssue(ctx context.Context, inst *models.Instance, match catalogue.Match, reason string) error {
+	plan, err := models.GetPlan(ctx, inst.Deployment, match.Tier)
+	if err != nil {
+		return fmt.Errorf("no plan for %s/%s: %w", inst.Deployment, match.Tier, err)
+	}
+	granted := models.Config{
+		Servers:  match.Servers,
+		Features: models.Features(match.Features).OrEmpty(),
+	}
+	limits, _, err := catalogue.Resolve(ctx, plan, granted)
+	if err != nil {
+		return err
+	}
+	if err := models.UpsertEntitlement(ctx, models.Entitlement{
+		InstanceID:     inst.InstanceID,
+		AccountID:      inst.AccountID,
+		Deployment:     inst.Deployment,
+		Tier:           match.Tier,
+		Term:           match.Term,
+		Desired:        granted,
+		Granted:        granted,
+		ResolvedLimits: limits,
+	}); err != nil {
+		return err
+	}
+
+	lic, err := licensing.Issue(ctx, licensing.IssueInput{
+		InstanceID: inst.InstanceID,
+		Tier:       match.Tier,
+		Term:       match.Term,
+		Reason:     reason,
+		IssuedBy:   "paddle",
+	})
+	if err != nil {
+		return fmt.Errorf("issue for %s: %w", inst.InstanceID, err)
+	}
+	deliver(ctx, inst, lic, billingEmailFor(ctx, inst.AccountID))
+	return nil
+}
+
+// handleCanceled marks the SUBSCRIPTION cancelled and takes NO licence action.
+//
+// The instance stays active until its licence expires, when the existing
+// lifecycle sweep lapses it. Flipping the instance to cancelled here would stop
+// inject.Reconcile and the sweep repairing a licence that is still valid — the
+// opposite of "keeps working until it expires".
+func handleCanceled(ctx context.Context, ev Event) error {
+	d, err := decode[subscriptionData](ev)
+	if err != nil {
+		return err
+	}
+	if _, err := db.Admin("subscriptions").UpdateOne(ctx,
+		bson.M{"paddle_subscription_id": d.ID},
+		bson.M{"$set": bson.M{"status": models.SubCanceled}}); err != nil {
+		return err
+	}
+	if to := billingEmailFor(ctx, d.CustomData.AccountID); to != "" {
+		_ = mail.SendCancelled(to, instanceNameFor(ctx, d.CustomData.InstanceID))
+	}
+	return nil
+}
+
+// handlePastDue flags the subscription and notifies, but leaves the licence
+// alone. Dunning is Paddle's; ours is not to punish a retryable card failure.
+func handlePastDue(ctx context.Context, ev Event) error {
+	d, err := decode[subscriptionData](ev)
+	if err != nil {
+		return err
+	}
+	if _, err := db.Admin("subscriptions").UpdateOne(ctx,
+		bson.M{"paddle_subscription_id": d.ID},
+		bson.M{"$set": bson.M{"status": models.SubPastDue}}); err != nil {
+		return err
+	}
+	if to := billingEmailFor(ctx, d.CustomData.AccountID); to != "" {
+		_ = mail.SendPastDue(to, instanceNameFor(ctx, d.CustomData.InstanceID))
+	}
+	return nil
+}
+
+// handleCustomerUpdated syncs the billing email onto the account.
+func handleCustomerUpdated(ctx context.Context, ev Event) error {
+	d, err := decode[struct {
+		ID    string `json:"id"`
+		Email string `json:"email"`
+	}](ev)
+	if err != nil {
+		return err
+	}
+	if d.ID == "" || d.Email == "" {
+		return nil
+	}
+	_, err = db.Admin("accounts").UpdateOne(ctx,
+		bson.M{"paddle_customer_id": d.ID},
+		bson.M{"$set": bson.M{"billing_email": d.Email}})
+	return err
+}
+
+// IssueForInstance issues from an instance's recorded subscription. Called when
+// a self-hosted customer finally links a placeholder they have already paid for.
+func IssueForInstance(ctx context.Context, instanceID string) error {
+	var sub models.Subscription
+	if err := db.Admin("subscriptions").FindOne(ctx,
+		bson.M{"instance_id": instanceID, "status": models.SubActive}).Decode(&sub); err != nil {
+		return fmt.Errorf("no active subscription for %s: %w", instanceID, err)
+	}
+	var inst models.Instance
+	if err := db.Admin("admin_instances").FindOne(ctx,
+		bson.M{"instance_id": instanceID}).Decode(&inst); err != nil {
+		return err
+	}
+	items := make([]catalogue.Item, 0, len(sub.Items))
+	for _, it := range sub.Items {
+		items = append(items, catalogue.Item{PriceID: it.PriceID, Quantity: it.Quantity})
+	}
+	match, err := catalogue.ResolveItems(ctx, paddle.Get().Env(), items)
+	if err != nil {
+		return err
+	}
+	return promoteAndIssue(ctx, &inst, match, models.ReasonNew)
+}
+
+func toSubItems(items []catalogue.Item) []models.SubItem {
+	out := make([]models.SubItem, 0, len(items))
+	for _, it := range items {
+		out = append(out, models.SubItem{PriceID: it.PriceID, Quantity: it.Quantity})
+	}
+	return out
+}
+
+func upsertSubscription(ctx context.Context, sub models.Subscription) error {
+	_, err := db.Admin("subscriptions").UpdateOne(ctx,
+		bson.M{"paddle_subscription_id": sub.PaddleSubscriptionID},
+		bson.M{"$set": bson.M{
+			"account_id":         sub.AccountID,
+			"instance_id":        sub.InstanceID,
+			"tier":               sub.Tier,
+			"term":               sub.Term,
+			"status":             sub.Status,
+			"current_period_end": sub.CurrentPeriodEnd,
+			"items":              sub.Items,
+		}, "$setOnInsert": bson.M{
+			"subscription_id":        uuid.NewString(),
+			"paddle_subscription_id": sub.PaddleSubscriptionID,
+		}},
+		options.UpdateOne().SetUpsert(true))
+	return err
+}
+
+// billingEmailFor reads the account's billing email for self-hosted delivery.
+func billingEmailFor(ctx context.Context, accountID string) string {
+	var acc models.Account
+	if err := db.Admin("accounts").FindOne(ctx,
+		bson.M{"account_id": accountID}).Decode(&acc); err != nil {
+		return ""
+	}
+	return acc.BillingEmail
+}
+
+// instanceNameFor is a best-effort display name for an email subject.
+func instanceNameFor(ctx context.Context, instanceID string) string {
+	var inst models.Instance
+	if err := db.Admin("admin_instances").FindOne(ctx,
+		bson.M{"instance_id": instanceID}).Decode(&inst); err != nil || inst.Name == "" {
+		return "your instance"
+	}
+	return inst.Name
+}

admin/internal/billing/transaction.go

@@ -0,0 +1,124 @@
+package billing
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/mrhid6/vantage/admin/internal/catalogue"
+	"github.com/mrhid6/vantage/admin/internal/db"
+	"github.com/mrhid6/vantage/admin/internal/models"
+	"github.com/mrhid6/vantage/admin/internal/paddle"
+	"go.mongodb.org/mongo-driver/v2/bson"
+)
+
+type transactionData struct {
+	ID             string `json:"id"`
+	SubscriptionID string `json:"subscription_id"`
+	Origin         string `json:"origin"`
+	Items          []struct {
+		Price struct {
+			ID string `json:"id"`
+		} `json:"price"`
+		Quantity int `json:"quantity"`
+	} `json:"items"`
+}
+
+// handleTransactionCompleted issues the next term's licence on a renewal.
+//
+// A renewal is the one moment a scheduled REDUCTION takes effect: the customer's
+// desired (smaller) configuration becomes granted. Mid-term reductions never
+// shrink a live licence. On a first charge (origin not recurring) the
+// subscription.created/updated handler already issued, so this is a no-op to
+// avoid a double issue.
+func handleTransactionCompleted(ctx context.Context, ev Event) error {
+	d, err := decode[transactionData](ev)
+	if err != nil {
+		return err
+	}
+	if d.Origin != "subscription_recurring" {
+		return nil
+	}
+	if d.SubscriptionID == "" {
+		return fmt.Errorf("renewal transaction %s has no subscription_id", d.ID)
+	}
+
+	var sub models.Subscription
+	if err := db.Admin("subscriptions").FindOne(ctx,
+		bson.M{"paddle_subscription_id": d.SubscriptionID}).Decode(&sub); err != nil {
+		return fmt.Errorf("renewal for unknown subscription %s: %w", d.SubscriptionID, err)
+	}
+
+	var inst models.Instance
+	if err := db.Admin("admin_instances").FindOne(ctx,
+		bson.M{"instance_id": sub.InstanceID}).Decode(&inst); err != nil {
+		return fmt.Errorf("renewal names unknown instance %s: %w", sub.InstanceID, err)
+	}
+
+	// Prefer the transaction's own item list (authoritative for this period);
+	// fall back to the subscription's recorded items.
+	items := make([]catalogue.Item, 0, len(d.Items))
+	for _, it := range d.Items {
+		items = append(items, catalogue.Item{PriceID: it.Price.ID, Quantity: it.Quantity})
+	}
+	if len(items) == 0 {
+		for _, it := range sub.Items {
+			items = append(items, catalogue.Item{PriceID: it.PriceID, Quantity: it.Quantity})
+		}
+	}
+	match, err := catalogue.ResolveItems(ctx, paddle.Get().Env(), items)
+	if err != nil {
+		return fmt.Errorf("resolve renewal items for %s: %w", d.SubscriptionID, err)
+	}
+
+	// Collapse a scheduled reduction: desired becomes granted, and the pending
+	// marker is cleared, since a new term has begun. This is the only place a
+	// licence ever gets a smaller cap.
+	if err := promoteScheduledReduction(ctx, inst.InstanceID); err != nil {
+		return err
+	}
+
+	// Issue the next term. Renewal resets relink_count inside licensing.Issue.
+	if err := promoteAndIssue(ctx, &inst, match, models.ReasonRenewal); err != nil {
+		return err
+	}
+
+	// Clear lifecycle notices so the next term starts the sequence fresh (mirrors
+	// the self-serve renew path).
+	_, _ = db.Admin("admin_instances").UpdateOne(ctx,
+		bson.M{"instance_id": inst.InstanceID},
+		bson.M{"$unset": bson.M{"notices_sent": ""}})
+	return nil
+}
+
+// promoteScheduledReduction collapses a pending reduction into granted at
+// renewal and clears scheduled_change_at. A no-op when nothing is pending — the
+// match resolved from the renewal's items is authoritative either way, so this
+// only keeps the entitlement's own bookkeeping honest.
+func promoteScheduledReduction(ctx context.Context, instanceID string) error {
+	ent, err := models.GetEntitlement(ctx, instanceID)
+	if err != nil {
+		return nil // no entitlement to reconcile
+	}
+	if ent.ScheduledChangeAt == nil {
+		return nil
+	}
+	ent.Granted = ent.Desired
+	ent.ScheduledChangeAt = nil
+	return models.UpsertEntitlement(ctx, *ent)
+}
+
+// handlePaymentFailed records the failure for staff visibility. No licence
+// action — the licence runs to its (grace-padded) expiry and Paddle retries.
+func handlePaymentFailed(ctx context.Context, ev Event) error {
+	d, err := decode[transactionData](ev)
+	if err != nil {
+		return err
+	}
+	if d.SubscriptionID == "" {
+		return nil
+	}
+	_, err = db.Admin("subscriptions").UpdateOne(ctx,
+		bson.M{"paddle_subscription_id": d.SubscriptionID},
+		bson.M{"$set": bson.M{"status": models.SubPastDue}})
+	return err
+}

admin/internal/config/config.go

@@ -29,6 +29,10 @@ type Config struct {
 	Addr            string
 	ReapAfter       time.Duration
 
+	PaddleEnv           string // "sandbox" or "production"
+	PaddleAPIKey        string
+	PaddleWebhookSecret string
+
 	SMTPHost     string
 	SMTPPort     string
 	SMTPFrom     string
@@ -75,6 +79,10 @@ func Load() (Config, error) {
 		SMTPFrom:     os.Getenv("SMTP_FROM"),
 		SMTPUsername: os.Getenv("SMTP_USERNAME"),
 		SMTPPassword: os.Getenv("SMTP_PASSWORD"),
+
+		PaddleEnv:           envOr("PADDLE_ENV", "sandbox"),
+		PaddleAPIKey:        os.Getenv("PADDLE_API_KEY"),
+		PaddleWebhookSecret: os.Getenv("PADDLE_WEBHOOK_SECRET"),
 	}
 
 	var missing []string
@@ -85,6 +93,10 @@ func Load() (Config, error) {
 		"LICENSE_SIGNING_KEY": c.SigningKey,
 		"PUBLIC_URL":          c.PublicURL,
 		"ADMIN_ORIGIN":        os.Getenv("ADMIN_ORIGIN"),
+		// An unverified webhook endpoint is one anyone can issue licences
+		// through, so the secret and API key are boot-required.
+		"PADDLE_API_KEY":        c.PaddleAPIKey,
+		"PADDLE_WEBHOOK_SECRET": c.PaddleWebhookSecret,
 	} {
 		if v == "" {
 			missing = append(missing, name)

admin/internal/db/db.go

@@ -85,6 +85,7 @@ func EnsureIndexes(ctx context.Context) error {
 		{"accounts", "account_id"},
 		{"admin_instances", "instance_id"},
 		{"licenses", "license_id"},
+		{"paddle_events", "event_id"},
 		{"staff_users", "email"},
 		{"customer_users", "email"},
 	}

admin/internal/lifecycle/lifecycle.go

@@ -172,4 +172,74 @@ func runOnce(ctx context.Context) {
 	if err := Run(runCtx); err != nil {
 		log.Printf("lifecycle: %v", err)
 	}
+	sweepAwaitingLink(runCtx)
+}
+
+// Awaiting-link reminder keys.
+const (
+	noticeLink24 = "link_24"
+	noticeLink72 = "link_72"
+)
+
+// sweepAwaitingLink chases self-hosted instances that were paid for but never
+// linked: the subscription exists, the instance is still a placeholder. It
+// emails a reminder at 24h and again at 72h. The staff dashboard already flags
+// 48h; this is the active chasing on top of that. It never issues or deletes.
+func sweepAwaitingLink(ctx context.Context) {
+	cur, err := db.Admin("admin_instances").Find(ctx, bson.M{
+		"deployment":  license.DeploymentSelfHosted,
+		"placeholder": true,
+		"status":      models.StatusAwaitingLink,
+	})
+	if err != nil {
+		return
+	}
+	var instances []models.Instance
+	if err := cur.All(ctx, &instances); err != nil {
+		return
+	}
+	now := time.Now().UTC()
+	for _, inst := range instances {
+		// Only chase placeholders a customer has actually paid for.
+		n, err := db.Admin("subscriptions").CountDocuments(ctx,
+			bson.M{"instance_id": inst.InstanceID, "status": models.SubActive})
+		if err != nil || n == 0 {
+			continue
+		}
+		if !mail.Enabled() {
+			continue
+		}
+		to := accountEmail(ctx, inst.AccountID)
+		if to == "" {
+			continue
+		}
+		age := now.Sub(inst.CreatedAt)
+		var due string
+		if age > 72*time.Hour && !slices.Contains(inst.NoticesSent, noticeLink72) {
+			due = noticeLink72
+		} else if age > 24*time.Hour && !slices.Contains(inst.NoticesSent, noticeLink24) {
+			due = noticeLink24
+		}
+		if due == "" {
+			continue
+		}
+		if err := mail.SendLinkReminder(to, inst.Name); err != nil {
+			log.Printf("lifecycle: link reminder %s for %s: %v", due, inst.InstanceID, err)
+			continue
+		}
+		if _, err := db.Admin("admin_instances").UpdateOne(ctx,
+			bson.M{"instance_id": inst.InstanceID},
+			bson.M{"$addToSet": bson.M{"notices_sent": due}}); err != nil {
+			log.Printf("lifecycle: record link notice %s for %s: %v", due, inst.InstanceID, err)
+		}
+	}
+}
+
+func accountEmail(ctx context.Context, accountID string) string {
+	var acct models.Account
+	if err := db.Admin("accounts").FindOne(ctx,
+		bson.M{"account_id": accountID}).Decode(&acct); err != nil {
+		return ""
+	}
+	return acct.BillingEmail
 }

admin/internal/mail/mail.go

@@ -164,6 +164,32 @@ func SendLicense(to, instanceName, blob string) error {
 			instanceName, blob))
 }
 
+// SendCancelled confirms a cancellation and states what stays true: the licence
+// keeps working until it expires, then the instance degrades to read-only.
+func SendCancelled(to, instanceName string) error {
+	return send(to, "Your Vantage subscription is cancelled",
+		fmt.Sprintf("Your subscription for %s is cancelled.\n\n"+
+			"Your instance keeps working until the current licence expires. After "+
+			"that, monitors keep running but changes are disabled.\n", instanceName))
+}
+
+// SendPastDue notifies of a failed charge without alarming: the licence is
+// untouched while Paddle retries the card.
+func SendPastDue(to, instanceName string) error {
+	return send(to, "Payment failed for your Vantage subscription",
+		fmt.Sprintf("A payment for %s failed.\n\n"+
+			"Your instance is unaffected while the card is retried. Update your "+
+			"payment method from the billing portal.\n", instanceName))
+}
+
+// SendLinkReminder chases a self-hosted customer who paid but never linked.
+func SendLinkReminder(to, instanceName string) error {
+	return send(to, "Finish setting up "+instanceName,
+		fmt.Sprintf("Your subscription for %s is active, but the instance is not "+
+			"linked yet.\n\nPaste your install's ID in the portal to receive your "+
+			"licence.\n", instanceName))
+}
+
 // SendInstanceReady tells a customer their cloud instance exists, where it is,
 // and when its licence runs out.
 //

admin/internal/models/models.go

@@ -77,6 +77,21 @@ const (
 	ReasonEntitlementChange = "entitlement_change"
 )
 
+// Subscription statuses, mirrored from Paddle. Ours, not a vendor SDK's, so the
+// billing package does not import anything Paddle.
+const (
+	SubActive   = "active"
+	SubCanceled = "canceled"
+	SubPastDue  = "past_due"
+	SubTrialing = "trialing"
+)
+
+// Billing terms. These match catalogue price-ID keys and license.TermsFor.
+const (
+	TermMonthly = "monthly"
+	TermAnnual  = "annual"
+)
+
 // MaxRelinksPerTerm is the customer-facing relink cap.
 //
 // This is an abuse SIGNAL, not abuse prevention — offline licences cannot be
@@ -128,6 +143,10 @@ type Instance struct {
 	// clears it, so the next term starts the sequence again. It is what stops a
 	// restart re-sending a notice.
 	NoticesSent []string  `bson:"notices_sent,omitempty" json:"notices_sent,omitempty"`
+	// Placeholder is true while a self-hosted instance row exists only so a
+	// checkout has something to attach custom_data to, before the customer has
+	// pasted their install's real UUID. Cleared when the instance is linked.
+	Placeholder bool      `bson:"placeholder,omitempty" json:"placeholder,omitempty"`
 	CreatedAt   time.Time `bson:"created_at" json:"created_at"`
 }
 
@@ -158,11 +177,32 @@ type Subscription struct {
 	AccountID            string        `bson:"account_id" json:"account_id"`
 	InstanceID           string        `bson:"instance_id,omitempty" json:"instance_id,omitempty"`
 	PaddleSubscriptionID string        `bson:"paddle_subscription_id,omitempty" json:"paddle_subscription_id,omitempty"`
-	PaddlePriceID        string        `bson:"paddle_price_id,omitempty" json:"paddle_price_id,omitempty"`
 	Tier                 string        `bson:"tier" json:"tier"`
 	Term                 string        `bson:"term" json:"term"`
 	Status               string        `bson:"status" json:"status"`
 	CurrentPeriodEnd     time.Time     `bson:"current_period_end" json:"current_period_end"`
+	// Items is the full line-item list. Spec 7 made a subscription several
+	// prices — a base, a per-server unit at quantity N, an item per paid
+	// feature — so a single price ID can no longer describe it.
+	Items []SubItem `bson:"items,omitempty" json:"items,omitempty"`
+}
+
+// SubItem is one line of a subscription: a price and its quantity, the shape
+// catalogue.ResolveItems reads back into a plan and configuration.
+type SubItem struct {
+	PriceID  string `bson:"price_id" json:"price_id"`
+	Quantity int    `bson:"quantity" json:"quantity"`
+}
+
+// PaddleEvent is the idempotency record for one webhook delivery. The unique
+// index on EventID is what makes a retry a no-op rather than a second licence.
+type PaddleEvent struct {
+	ID          bson.ObjectID `bson:"_id,omitempty" json:"-"`
+	EventID     string        `bson:"event_id" json:"event_id"`
+	EventType   string        `bson:"event_type" json:"event_type"`
+	ReceivedAt  time.Time     `bson:"received_at" json:"received_at"`
+	ProcessedAt *time.Time    `bson:"processed_at,omitempty" json:"processed_at,omitempty"`
+	Error       string        `bson:"error,omitempty" json:"error,omitempty"`
 }
 
 // Plan is the authoritative definition of one (deployment, tier) pair, seeded

admin/internal/models/paddle_events.go

@@ -0,0 +1,48 @@
+package models
+
+import (
+	"context"
+	"time"
+
+	"github.com/mrhid6/vantage/admin/internal/db"
+	"go.mongodb.org/mongo-driver/v2/bson"
+	"go.mongodb.org/mongo-driver/v2/mongo"
+)
+
+// ClaimEvent records an event ID before it is processed and reports whether THIS
+// call is the one that claimed it.
+//
+// The unique index on event_id turns a duplicate insert into a duplicate-key
+// error, which is the signal that another delivery of the same event already
+// owns it — so this returns (false, nil) and the caller answers 200 without
+// acting. A genuine error returns (false, err).
+func ClaimEvent(ctx context.Context, eventID, eventType string) (bool, error) {
+	_, err := db.Admin("paddle_events").InsertOne(ctx, PaddleEvent{
+		EventID:    eventID,
+		EventType:  eventType,
+		ReceivedAt: time.Now().UTC(),
+	})
+	if err == nil {
+		return true, nil
+	}
+	if mongo.IsDuplicateKeyError(err) {
+		return false, nil
+	}
+	return false, err
+}
+
+// MarkEventProcessed stamps success, or records the error for staff visibility.
+// A failed event keeps no processed_at, so a retry re-runs it.
+func MarkEventProcessed(ctx context.Context, eventID string, procErr error) error {
+	set := bson.M{}
+	if procErr != nil {
+		set["error"] = procErr.Error()
+	} else {
+		now := time.Now().UTC()
+		set["processed_at"] = now
+		set["error"] = ""
+	}
+	_, err := db.Admin("paddle_events").UpdateOne(ctx,
+		bson.M{"event_id": eventID}, bson.M{"$set": set})
+	return err
+}

admin/internal/paddle/client.go

@@ -0,0 +1,54 @@
+// Package paddle is the only place that talks to Paddle. Everything outside it
+// depends on the Client interface and our own types, never on Paddle's wire
+// shapes — so a change at Paddle is confined to http.go, and the billing package
+// can be reasoned about without knowing Paddle exists.
+//
+// It is a thin REST client rather than the vendor SDK on purpose: the surface we
+// need is two calls, and a hand-rolled client has no version-drift risk and no
+// dependency to keep in go.sum.
+package paddle
+
+import "context"
+
+// LineItem is one price at a quantity, the shape both a checkout and a
+// subscription update are built from.
+type LineItem struct {
+	PriceID  string
+	Quantity int
+}
+
+// Client is the narrow slice of Paddle admin needs. Checkout itself happens in
+// the browser via paddle-js; the server only updates an existing subscription
+// and mints a portal session.
+type Client interface {
+	// UpdateSubscriptionItems replaces a subscription's items, prorated
+	// immediately by Paddle. This is the one outbound mutation, used when a
+	// customer changes their server count or features on an existing plan.
+	UpdateSubscriptionItems(ctx context.Context, paddleSubscriptionID string, items []LineItem) error
+	// PortalSession returns a customer-portal URL for managing billing.
+	PortalSession(ctx context.Context, paddleCustomerID string) (string, error)
+	// Env is "sandbox" or "production", the same value catalogue price lookups
+	// are keyed on.
+	Env() string
+}
+
+var current Client
+
+// Init constructs the client from config and stores it. Called once at boot.
+func Init(apiKey, env string) (Client, error) {
+	c, err := newHTTPClient(apiKey, env)
+	if err != nil {
+		return nil, err
+	}
+	current = c
+	return c, nil
+}
+
+// Get returns the client initialised at boot. Panics if unset, which can only
+// happen if a caller runs before Init — a programming error, not a runtime one.
+func Get() Client {
+	if current == nil {
+		panic("paddle.Get before paddle.Init")
+	}
+	return current
+}

admin/internal/paddle/http.go

@@ -0,0 +1,120 @@
+package paddle
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"time"
+)
+
+// httpClient is the only implementation of Client. It is the single place that
+// knows Paddle's base URLs, auth header and request shapes — swap the whole
+// vendor here without the rest of the tree noticing.
+type httpClient struct {
+	apiKey string
+	env    string
+	base   string
+	http   *http.Client
+}
+
+func newHTTPClient(apiKey, env string) (Client, error) {
+	if apiKey == "" {
+		return nil, fmt.Errorf("paddle: empty API key")
+	}
+	base := "https://sandbox-api.paddle.com"
+	if env == "production" {
+		base = "https://api.paddle.com"
+	}
+	return &httpClient{
+		apiKey: apiKey,
+		env:    env,
+		base:   base,
+		http:   &http.Client{Timeout: 20 * time.Second},
+	}, nil
+}
+
+func (c *httpClient) Env() string { return c.env }
+
+// do sends a JSON request and decodes the `data` envelope Paddle wraps every
+// response in. A non-2xx is returned as an error carrying the body, so a
+// configuration or auth failure is loud rather than silent.
+func (c *httpClient) do(ctx context.Context, method, path string, body any, out any) error {
+	var buf io.Reader
+	if body != nil {
+		b, err := json.Marshal(body)
+		if err != nil {
+			return fmt.Errorf("paddle: marshal %s %s: %w", method, path, err)
+		}
+		buf = bytes.NewReader(b)
+	}
+	req, err := http.NewRequestWithContext(ctx, method, c.base+path, buf)
+	if err != nil {
+		return fmt.Errorf("paddle: build %s %s: %w", method, path, err)
+	}
+	req.Header.Set("Authorization", "Bearer "+c.apiKey)
+	req.Header.Set("Content-Type", "application/json")
+
+	res, err := c.http.Do(req)
+	if err != nil {
+		return fmt.Errorf("paddle: %s %s: %w", method, path, err)
+	}
+	defer res.Body.Close()
+	raw, _ := io.ReadAll(res.Body)
+	if res.StatusCode < 200 || res.StatusCode >= 300 {
+		return fmt.Errorf("paddle: %s %s returned %d: %s", method, path, res.StatusCode, string(raw))
+	}
+	if out == nil {
+		return nil
+	}
+	if err := json.Unmarshal(raw, out); err != nil {
+		return fmt.Errorf("paddle: decode %s %s: %w", method, path, err)
+	}
+	return nil
+}
+
+type updateSubscriptionRequest struct {
+	Items                []reqItem `json:"items"`
+	ProrationBillingMode string    `json:"proration_billing_mode"`
+}
+
+type reqItem struct {
+	PriceID  string `json:"price_id"`
+	Quantity int    `json:"quantity"`
+}
+
+func (c *httpClient) UpdateSubscriptionItems(ctx context.Context, subID string, items []LineItem) error {
+	if subID == "" {
+		return fmt.Errorf("paddle: empty subscription id")
+	}
+	reqItems := make([]reqItem, 0, len(items))
+	for _, it := range items {
+		reqItems = append(reqItems, reqItem{PriceID: it.PriceID, Quantity: it.Quantity})
+	}
+	return c.do(ctx, http.MethodPatch, "/subscriptions/"+subID, updateSubscriptionRequest{
+		Items:                reqItems,
+		ProrationBillingMode: "prorated_immediately",
+	}, nil)
+}
+
+func (c *httpClient) PortalSession(ctx context.Context, customerID string) (string, error) {
+	if customerID == "" {
+		return "", fmt.Errorf("paddle: empty customer id")
+	}
+	var out struct {
+		Data struct {
+			URLs struct {
+				General struct {
+					Overview string `json:"overview"`
+				} `json:"general"`
+			} `json:"urls"`
+		} `json:"data"`
+	}
+	if err := c.do(ctx, http.MethodPost,
+		"/customers/"+customerID+"/portal-sessions", struct{}{}, &out); err != nil {
+		return "", err
+	}
+	return out.Data.URLs.General.Overview, nil
+}

admin/internal/paddle/webhook.go

@@ -0,0 +1,42 @@
+package paddle
+
+import (
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/hex"
+	"strings"
+)
+
+// VerifySignature checks a raw webhook body against the Paddle-Signature header.
+//
+// Paddle signs an HMAC-SHA256 over "ts:body", carried as "ts=<unix>;h1=<hex>".
+// It uses a constant-time compare and never logs the secret. A false return is
+// always a 401 with nothing processed — an unverified body could be anyone
+// claiming a subscription was paid for.
+func VerifySignature(secret, header string, body []byte) bool {
+	if secret == "" || header == "" {
+		return false
+	}
+	var ts, h1 string
+	for _, part := range strings.Split(header, ";") {
+		k, v, ok := strings.Cut(part, "=")
+		if !ok {
+			continue
+		}
+		switch k {
+		case "ts":
+			ts = v
+		case "h1":
+			h1 = v
+		}
+	}
+	if ts == "" || h1 == "" {
+		return false
+	}
+	mac := hmac.New(sha256.New, []byte(secret))
+	mac.Write([]byte(ts))
+	mac.Write([]byte(":"))
+	mac.Write(body)
+	want := hex.EncodeToString(mac.Sum(nil))
+	return hmac.Equal([]byte(want), []byte(h1))
+}

adminsite/Dockerfile

@@ -19,6 +19,13 @@ ENV NEXT_PUBLIC_ADMIN_API_URL=$NEXT_PUBLIC_ADMIN_API_URL
 ARG NEXT_PUBLIC_ADMIN_ENV=production
 ENV NEXT_PUBLIC_ADMIN_ENV=$NEXT_PUBLIC_ADMIN_ENV
 
+# Browser checkout. The client token and environment are baked in, never
+# fetched, so a production build cannot load a sandbox token by accident.
+ARG NEXT_PUBLIC_PADDLE_CLIENT_TOKEN=
+ENV NEXT_PUBLIC_PADDLE_CLIENT_TOKEN=$NEXT_PUBLIC_PADDLE_CLIENT_TOKEN
+ARG NEXT_PUBLIC_PADDLE_ENV=sandbox
+ENV NEXT_PUBLIC_PADDLE_ENV=$NEXT_PUBLIC_PADDLE_ENV
+
 RUN npm run build
 
 FROM node:26-alpine AS runner

adminsite/app/(customer)/purchase/PurchaseForm.tsx

@@ -0,0 +1,131 @@
+"use client";
+
+import { useState } from "react";
+import { useRouter } from "next/navigation";
+import { useMutation, useQuery } from "@tanstack/react-query";
+import { ApiError, api, lineItemsFor } from "@/lib/api";
+import { Button } from "@/components/Button";
+import { Field } from "@/components/Field";
+import { CheckoutButton } from "@/components/CheckoutButton";
+import PlanConfigurator, { type PlanChoice } from "@/components/PlanConfigurator";
+
+/*
+ * Three visible steps: name (creates a placeholder), configure + pay, then link
+ * the real install UUID. The placeholder exists before payment so the webhook
+ * has something to attach custom_data to; the licence is only issued once the
+ * install's real UUID is known.
+ */
+export function PurchaseForm() {
+    const router = useRouter();
+    const account = useQuery({ queryKey: ["account"], queryFn: api.account });
+    const options = useQuery({ queryKey: ["checkout-options"], queryFn: api.checkoutOptions });
+
+    const [name, setName] = useState("");
+    const [placeholderId, setPlaceholderId] = useState<string | null>(null);
+    const [uuid, setUuid] = useState("");
+    const [error, setError] = useState<string | null>(null);
+    const [choice, setChoice] = useState<PlanChoice>({
+        tier: "professional",
+        term: "annual", // self-hosted is annual only
+        servers: 3,
+        features: [],
+    });
+
+    const create = useMutation({
+        mutationFn: () => api.createSelfHosted(name.trim()),
+        onSuccess: (r) => setPlaceholderId(r.instance_id),
+        onError: (e) => setError(e instanceof ApiError ? e.message : "Could not start. Try again."),
+    });
+
+    const claim = useMutation({
+        mutationFn: () => api.claimLink(placeholderId!, uuid.trim()),
+        onSuccess: () => router.push("/"),
+        onError: (e) => setError(e instanceof ApiError ? e.message : "Could not link. Try again."),
+    });
+
+    const accountId = account.data?.account.account_id ?? "";
+    const items =
+        options.data && placeholderId
+            ? lineItemsFor(options.data, choice, "self_hosted")
+            : [];
+
+    // Step 1 — name.
+    if (!placeholderId) {
+        return (
+            <form
+                className="grid max-w-md gap-4"
+                onSubmit={(e) => {
+                    e.preventDefault();
+                    setError(null);
+                    if (name.trim()) create.mutate();
+                }}
+            >
+                <Field
+                    label="Instance name"
+                    value={name}
+                    onChange={(e) => setName(e.target.value)}
+                    placeholder="Northgate Systems"
+                    required
+                    error={error ?? undefined}
+                />
+                <Button type="submit" disabled={create.isPending || !name.trim()}>
+                    {create.isPending ? "Starting…" : "Continue"}
+                </Button>
+            </form>
+        );
+    }
+
+    // Step 2 + 3 — configure & pay, then link.
+    return (
+        <div className="grid max-w-2xl gap-6">
+            <section className="rounded-lg border border-rule bg-panel p-4">
+                <h2 className="mb-3 text-[0.95rem] font-medium text-ink">Configure</h2>
+                {options.data ? (
+                    <PlanConfigurator
+                        deployment="self_hosted"
+                        value={choice}
+                        plans={options.data.plans}
+                        catalogue={options.data.catalogue}
+                        onChange={setChoice}
+                    />
+                ) : (
+                    <p className="text-[0.85rem] text-ink-3">Loading plans…</p>
+                )}
+                <div className="mt-4">
+                    <CheckoutButton
+                        items={items}
+                        customData={{ account_id: accountId, instance_id: placeholderId }}
+                        disabled={!accountId || items.length === 0}
+                    />
+                </div>
+            </section>
+
+            <section className="rounded-lg border border-rule bg-panel p-4">
+                <h2 className="mb-1 text-[0.95rem] font-medium text-ink">Link your install</h2>
+                <p className="mb-3 text-[0.82rem] text-ink-3">
+                    After payment, paste the instance ID your Vantage install reports (Settings →
+                    Licence). Your licence is issued the moment it is linked.
+                </p>
+                <div className="grid gap-3">
+                    <Field
+                        label="Instance ID"
+                        value={uuid}
+                        onChange={(e) => setUuid(e.target.value)}
+                        placeholder="00000000-0000-0000-0000-000000000000"
+                        error={error ?? undefined}
+                    />
+                    <Button
+                        type="button"
+                        disabled={claim.isPending || !uuid.trim()}
+                        onClick={() => {
+                            setError(null);
+                            claim.mutate();
+                        }}
+                    >
+                        {claim.isPending ? "Linking…" : "Link and issue licence"}
+                    </Button>
+                </div>
+            </section>
+        </div>
+    );
+}

adminsite/app/(customer)/purchase/page.tsx

@@ -0,0 +1,18 @@
+import type { Metadata } from "next";
+import { PurchaseForm } from "./PurchaseForm";
+import { PageHeader } from "@/components/PageHeader";
+
+export const metadata: Metadata = { title: "Buy a self-hosted plan" };
+
+export default function PurchasePage() {
+    return (
+        <div className="grid gap-6">
+            <PageHeader
+                back={{ href: "/", label: "Overview" }}
+                title="Self-hosted plan"
+                subtitle="Name your instance, choose a plan, and pay. After payment, paste the ID your install reports to receive its licence. Self-hosted is billed annually."
+            />
+            <PurchaseForm />
+        </div>
+    );
+}

adminsite/components/CheckoutButton.tsx

@@ -0,0 +1,40 @@
+"use client";
+
+import { useState } from "react";
+import { initPaddle } from "@/lib/paddle";
+
+/* Opens the Paddle overlay with the resolved line items and custom_data. The
+ * items come from the configurator via catalogue pricing; custom_data is what
+ * lets the webhook route without a lookup table. */
+export function CheckoutButton({
+    items,
+    customData,
+    disabled,
+    label = "Continue to payment",
+}: {
+    items: { priceId: string; quantity: number }[];
+    customData: { account_id: string; instance_id: string };
+    disabled?: boolean;
+    label?: string;
+}) {
+    const [busy, setBusy] = useState(false);
+    async function open() {
+        setBusy(true);
+        const paddle = await initPaddle();
+        setBusy(false);
+        paddle?.Checkout.open({
+            items: items.map((i) => ({ priceId: i.priceId, quantity: i.quantity })),
+            customData,
+        });
+    }
+    return (
+        <button
+            type="button"
+            disabled={disabled || busy || items.length === 0}
+            onClick={open}
+            className="rounded border border-accent/50 px-3 py-1.5 text-[0.85rem] text-accent disabled:opacity-40"
+        >
+            {busy ? "Opening…" : label}
+        </button>
+    );
+}

adminsite/components/InstanceRecord.tsx

@@ -5,6 +5,7 @@ import clsx from "clsx";
 import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
 import { useEffect, useState } from "react";
 import { api, type Instance, type License } from "@/lib/api";
+import { ManageBillingButton } from "@/components/ManageBillingButton";
 import { daysRemaining, formatDate, licenceState, limitLabel } from "@/lib/format";
 import { StatePill } from "./StatePill";
 import { Button, LinkButton } from "./Button";
@@ -252,6 +253,8 @@ export function InstanceRecord({
                             {renew.isPending ? "Renewing…" : "Renew"}
                         </Button>
                     )}
+
+                    {cloud && <ManageBillingButton />}
                 </div>
             </div>
         </article>

adminsite/components/ManageBillingButton.tsx

@@ -0,0 +1,35 @@
+"use client";
+
+import { useState } from "react";
+import { ApiError, api } from "@/lib/api";
+import { Button } from "@/components/Button";
+
+/* Opens Paddle's hosted customer portal in a new tab. The account learns its
+ * paddle_customer_id from its first paid subscription's webhook, so this reports
+ * a plain message rather than erroring when there is no billing account yet. */
+export function ManageBillingButton() {
+    const [busy, setBusy] = useState(false);
+    const [note, setNote] = useState<string | null>(null);
+
+    async function open() {
+        setBusy(true);
+        setNote(null);
+        try {
+            const { url } = await api.billingPortal();
+            window.open(url, "_blank", "noopener");
+        } catch (e) {
+            setNote(e instanceof ApiError ? e.message : "Could not open billing.");
+        } finally {
+            setBusy(false);
+        }
+    }
+
+    return (
+        <span className="inline-flex items-center gap-2">
+            <Button type="button" variant="line" onClick={open} disabled={busy}>
+                {busy ? "Opening…" : "Manage billing"}
+            </Button>
+            {note && <span className="text-[0.78rem] text-ink-3">{note}</span>}
+        </span>
+    );
+}

adminsite/lib/api.ts

@@ -188,6 +188,51 @@ export interface EntitlementConfig {
     features: string[];
 }
 
+export interface CheckoutOptions {
+    plans: Plan[];
+    catalogue: CatalogueRow[];
+    env: "sandbox" | "production";
+}
+
+/*
+ * lineItemsFor builds the Paddle checkout items for a configuration, client-side
+ * from the catalogue already fetched. It mirrors the Go catalogue.LineItems and
+ * its billable() exactly: base is quantity 1; the per-server unit's quantity is
+ * servers MINUS the plan's base allowance (never charge for the base — the one
+ * subtraction, kept here to match the server); a feature contributes an item
+ * only when its row has a price in this environment/term.
+ */
+export function lineItemsFor(
+    opts: CheckoutOptions,
+    choice: { tier: Tier; term: Term; servers: number; features: string[] },
+    deployment: Deployment,
+): { priceId: string; quantity: number }[] {
+    const env = opts.env;
+    const plan = opts.plans.find((p) => p.deployment === deployment && p.tier === choice.tier);
+    if (!plan) return [];
+    const rows = opts.catalogue.filter(
+        (r) => r.deployment === deployment && r.tier === choice.tier,
+    );
+    const priceOf = (r: CatalogueRow) => r.price_ids?.[env]?.[choice.term] ?? "";
+    const base = plan.base_limits.max_servers;
+    const items: { priceId: string; quantity: number }[] = [];
+    for (const r of rows) {
+        const id = priceOf(r);
+        if (r.kind === "base") {
+            if (id) items.push({ priceId: id, quantity: 1 });
+        } else if (r.kind === "limit" && r.limit_key === "max_servers") {
+            // -1 base is unlimited: nothing metered. Otherwise charge servers over base.
+            const qty = base === -1 ? 0 : choice.servers - base;
+            if (qty > 0 && id) items.push({ priceId: id, quantity: qty });
+        } else if (r.kind === "feature" && r.feature_key) {
+            if (choice.features.includes(r.feature_key) && id) {
+                items.push({ priceId: id, quantity: 1 });
+            }
+        }
+    }
+    return items;
+}
+
 export interface Entitlement {
     instance_id: string;
     account_id: string;
@@ -269,6 +314,20 @@ export const api = {
     licenseBlobUrl: (id: string) => `${API_BASE}/api/instances/${id}/license/download`,
     subscriptions: () => req<Subscription[]>("/api/subscriptions"),
 
+    entitlement: (id: string) =>
+        req<{ entitlement: Entitlement; pending: boolean }>(`/api/instances/${id}/entitlement`),
+    checkoutOptions: () => req<CheckoutOptions>("/api/checkout/options"),
+    createSelfHosted: (name: string) =>
+        post<{ instance_id: string }>("/api/instances/self-hosted", { name }),
+    updateEntitlement: (
+        id: string,
+        body: { tier: Tier; term: Term; servers: number; features: string[] },
+    ) => put<{ entitlement: Entitlement; pending: boolean }>(`/api/instances/${id}/entitlement`, body),
+    claimLink: (placeholderId: string, instance_id: string) =>
+        post<{ instance_id: string; warning?: string }>(
+            `/api/instances/${placeholderId}/claim-link`, { instance_id }),
+    billingPortal: () => post<{ url: string }>("/api/billing/portal"),
+
     accountUsers: () => req<AccountUser[]>("/api/account/users"),
     invite: (email: string, role: AccountRole) =>
         post<{ invited: boolean }>("/api/account/users", { email, role }),

adminsite/lib/paddle.ts

@@ -0,0 +1,17 @@
+import { initializePaddle, type Paddle } from "@paddle/paddle-js";
+
+let cached: Promise<Paddle | undefined> | null = null;
+
+/* One Paddle instance for the app. The token and environment are baked into the
+ * build (NEXT_PUBLIC_*), never fetched, so a production build can never load a
+ * sandbox token by accident. */
+export function initPaddle(): Promise<Paddle | undefined> {
+    if (!cached) {
+        cached = initializePaddle({
+            environment:
+                (process.env.NEXT_PUBLIC_PADDLE_ENV as "sandbox" | "production") ?? "sandbox",
+            token: process.env.NEXT_PUBLIC_PADDLE_CLIENT_TOKEN ?? "",
+        });
+    }
+    return cached;
+}

adminsite/package-lock.json

@@ -8,6 +8,7 @@
             "name": "vantage-adminsite",
             "version": "0.1.0",
             "dependencies": {
+                "@paddle/paddle-js": "^1.6.4",
                 "@tanstack/react-query": "^5.51.1",
                 "clsx": "^2.1.1",
                 "next": "16.2.9",
@@ -1309,6 +1310,12 @@
                 "node": ">=12.4.0"
             }
         },
+        "node_modules/@paddle/paddle-js": {
+            "version": "1.6.4",
+            "resolved": "https://registry.npmjs.org/@paddle/paddle-js/-/paddle-js-1.6.4.tgz",
+            "integrity": "sha512-ncfnS6I8mCX6krZ3Sgz2iAYivGmhdI81yt9mT6prtPj4Ipd9J3M12LCJRUFL4FB7BYeeuV04c33RSEnbZUBCaA==",
+            "license": "Apache-2.0"
+        },
         "node_modules/@rtsao/scc": {
             "version": "1.1.0",
             "resolved": "https://registry.npmjs.org/@rtsao/scc/-/scc-1.1.0.tgz",

adminsite/package.json

@@ -9,11 +9,12 @@
         "lint": "next lint"
     },
     "dependencies": {
+        "@paddle/paddle-js": "^1.6.4",
+        "@tanstack/react-query": "^5.51.1",
+        "clsx": "^2.1.1",
         "next": "16.2.9",
         "react": "^18.3.1",
-        "react-dom": "^18.3.1",
-        "@tanstack/react-query": "^5.51.1",
-        "clsx": "^2.1.1"
+        "react-dom": "^18.3.1"
     },
     "devDependencies": {
         "@types/node": "^20.14.11",

claude.md

@@ -327,6 +327,7 @@ POST /auth/staff/login   /auth/login  /auth/logout
 POST /auth/signup                              # self-hosted only; honeypot + rate limited
 GET  /auth/verify?token=…
 POST /auth/accept-invite                       # an invitee sets their own password
+POST /api/paddle/webhook                       # Paddle events; signature-verified, idempotent, no session
 ```
 
 Customer-session (`/api`), every instance resolved through `ownedInstance`:
@@ -338,6 +339,11 @@ POST /instances/:id/renew                      # Free renewal; refuses outside t
 POST /instances/:id/claim-free                 # issue Free on a linked self-hosted instance
 POST /instances/link · /instances/:id/relink
 GET  /instances/:id/entitlement
+GET  /checkout/options                         # active plans + catalogue prices for the running PADDLE_ENV
+POST /instances/self-hosted                    # create a paid-checkout placeholder (awaiting_link, no licence)
+POST /instances/:id/claim-link                 # bind a paid placeholder to the real UUID and issue
+PUT  /instances/:id/entitlement                # set desired config; pushes line items to Paddle (owner|admin)
+POST /billing/portal                           # mint a Paddle customer-portal URL
 GET  /instances/:id/license · /instances/:id/license/download
 GET  /subscriptions
 GET,POST /account/users · PUT /account/users/:id/role · DELETE /account/users/:id
@@ -360,11 +366,17 @@ POST /instances/:id/issue · /instances/:id/relink
 GET  /licenses · /subscriptions · /audit · /plans · PUT /plans/:deployment/:tier
 GET,PUT /catalogue
 GET,PUT /instances/:id/entitlement
-GET  /health/injection
+GET  /health/injection · /health/billing
 ```
 
 **Customer endpoints answer 404, never 403, for another account's resource** — a 403 confirms the resource exists. Route-group guards in `adminsite/` mirror this, but the backend is the layer that matters.
 
+### Billing (Paddle)
+
+Paddle is merchant of record; `admin/internal/paddle` is a thin REST client (no vendor SDK) and the only place that talks to it. **Free is entirely outside Paddle** — the shipped self-serve Free flow owns its own renewal, so no £0 subscription exists; an account learns its `paddle_customer_id` from its first paid webhook. Checkout happens in the browser (`@paddle/paddle-js`, token baked into the adminsite build); the server only updates a live subscription (`PUT /instances/:id/entitlement`) and mints a portal session.
+
+`POST /api/paddle/webhook` is the **only** issuing path for paid plans: signature-verified with `PADDLE_WEBHOOK_SECRET` (boot-required), idempotent via `paddle_events`, and a function of the subscription's *current* line items — resolved back to a plan and configuration by `catalogue.ResolveItems`, so out-of-order delivery is correct by construction. A confirmed webhook promotes the entitlement `desired`→`granted` and signs from `granted` **only**; a checkout is built from `desired`. `subscription.canceled` and `past_due` take **no licence action** — the licence runs to its (grace-padded) expiry, then the existing lifecycle sweep lapses the instance. A renewal (`transaction.completed`, origin `subscription_recurring`) is the only moment a scheduled reduction collapses `desired` into `granted`. Self-hosted purchase creates a placeholder instance before payment (`POST /instances/self-hosted`); the licence is issued only once the customer pastes the install's real UUID (`POST /instances/:id/claim-link`), because a licence binds to that UUID.
+
 ## MongoDB Collections
 
 `servers` · `keys` · `assignments` · `orgs` · `users` · `org_oidc` · `settings` · `secrets` · `workflows` · `workflow_steps` · `workflow_runs` · `monitors` · `incidents` · `monitor_rollups` · `notification_channels` · `console_sessions` · `audit_logs` · `migrations`
@@ -381,7 +393,7 @@ Notes that are not obvious from the structs:
 - `console_sessions.token_consumed_at` is set atomically to enforce one-time use.
 - `users.auth_source` is `local`, `oidc` or `hq`. An `hq` user was projected from a Vantage HQ account and carries `hq_user_id`; HQ owns its role, password and existence.
 
-Admin's own database is separate and holds `accounts` · `admin_instances` · `licenses` · `subscriptions` · `plans` · `catalogue` · `entitlements` · `staff_users` · `customer_users` · `instance_members` · `admin_audit`. `instance_members` is unique on `(instance_id, customer_user_id)` — one person holds at most one user in one instance, which makes a grant idempotent-by-refusal rather than silently doubling a projection. It is an *index* of the control-plane rows, not the authority (see "Grants project, they do not federate"). Admin has no migrations collection; `models.Backfill` runs on every boot and is idempotent by filtering on the absence of what it writes.
+Admin's own database is separate and holds `accounts` · `admin_instances` · `licenses` · `subscriptions` · `plans` · `catalogue` · `entitlements` · `paddle_events` · `staff_users` · `customer_users` · `instance_members` · `admin_audit`. `paddle_events` is the webhook idempotency log, unique on `event_id`: an event is claimed there before processing, and a duplicate of a handled event is a 200 no-op. `instance_members` is unique on `(instance_id, customer_user_id)` — one person holds at most one user in one instance, which makes a grant idempotent-by-refusal rather than silently doubling a projection. It is an *index* of the control-plane rows, not the authority (see "Grants project, they do not federate"). Admin has no migrations collection; `models.Backfill` runs on every boot and is idempotent by filtering on the absence of what it writes.
 
 `plans` is keyed on `(deployment, tier)` — six rows, two deployments times three tiers — and holds base allowances only. **Every Paddle price ID lives in `catalogue`**, one row per priceable component (`base`, `limit`, `feature`), because a metered plan is priced by several prices and one map on a plan row cannot express that. `entitlements` holds one row per instance with `desired` beside `granted`: the checkout is built from `desired`, a licence is only ever signed from `granted`, and an abandoned checkout therefore leaves a `desired` that reached nothing. The two Free plans have **no catalogue rows at all**, which is what keeps Free outside Paddle.
 
@@ -613,6 +625,10 @@ git push origin main                                    # server + web deploy
 | `ADMIN_API_URL`      | Variable | **browser-reachable** admin URL, baked into **both** the `adminsite` and `site` images — `site/start` posts account signups straight to admin. Same footgun as `SITE_API_URL`: wrong here and every request fails at runtime with the not-connected panel. |
 | `ADMIN_ENV`          | Variable | `production` or `sandbox`; drives the persistent environment badge. Anything but `sandbox` reads as production.                                                                     |
 | `HQ_URL`             | Variable | optional; browser URL of the HQ portal, baked into `web` so an `hq`-sourced member links to where they are managed. Empty on self-hosted, which renders a plain label instead.       |
+| `PADDLE_CLIENT_TOKEN`| Variable | **browser** Paddle token, baked into the `adminsite` image for checkout. A repo-variable change pushes no commit, so rebuild `adminsite` manually via `workflow_dispatch` after editing it. |
+| `PADDLE_ENV`         | Variable | `sandbox` or `production`; baked into `adminsite` AND read by `admin` at runtime. Selects which `catalogue` price IDs are served, and must match on both sides.                       |
+| `PADDLE_API_KEY`     | Secret   | server-side Paddle key, read by `admin` at runtime. Boot-required.                                                                                                                    |
+| `PADDLE_WEBHOOK_SECRET` | Secret | webhook signature verification, read by `admin`. Boot-required — an unverified endpoint is one anyone can issue licences through.                                                     |
 
 ---
 

deploy/docker-compose.site.yml

@@ -57,6 +57,13 @@ services:
             SMTP_FROM: ${SMTP_FROM:-}
             APP_LOGIN_URL: ${APP_LOGIN_URL:-}
             FREE_INSTANCE_REAP_AFTER: "336h"
+            # Paddle billing. PADDLE_API_KEY and PADDLE_WEBHOOK_SECRET are
+            # boot-REQUIRED — an unverified webhook endpoint is one anyone can
+            # issue licences through. PADDLE_ENV selects which catalogue price
+            # IDs are served (sandbox|production).
+            PADDLE_ENV: ${PADDLE_ENV:-sandbox}
+            PADDLE_API_KEY: ${PADDLE_API_KEY:-}
+            PADDLE_WEBHOOK_SECRET: ${PADDLE_WEBHOOK_SECRET:-}
 
     # The staff and customer console, served at vantage-hq.hostxtra.co.uk.
     # ADMIN_API_URL is baked into the image at build time, not read here, so

docs/superpowers/specs/README.md

@@ -10,7 +10,7 @@ Build in this order. Specs 0a–5 were designed 2026-07-24; spec 6 on 2026-07-26
 | 2 | [instance-licensing](2026-07-24-instance-licensing-design.md) | [plan](../plans/2026-07-24-instance-licensing.md) | **shipped**, no grandfathering — existing cloud instances are read-only until admin backfills |
 | 3 | [admin-backend](2026-07-24-admin-backend-design.md) | [plan](../plans/2026-07-24-admin-backend.md) | **shipped**, verified end to end against scratch databases |
 | 4 | [admin-site](2026-07-24-admin-site-design.md) | — | ready to start |
-| 5 | [paddle-billing](2026-07-24-paddle-billing-design.md) | [plan](../plans/2026-07-26-paddle-billing.md) | ready to start, **but revised by 7** — its "signup migration off sitesvc" section is superseded by 6, and its single-price-per-subscription assumption by 7 |
+| 5 | [paddle-billing](2026-07-24-paddle-billing-design.md) | [plan](../plans/2026-07-27-paddle-billing.md) | **shipped (code)** — client, webhooks, checkout, entitlement update and portal built and compiled against spec-7's catalogue/entitlements; signup-migration dropped (done by 6). Live sandbox catalog + end-to-end pass is the operator's step. Old [2026-07-26 plan](../plans/2026-07-26-paddle-billing.md) superseded. |
 | 6 | [cloud-instance-creation](2026-07-26-cloud-instance-creation-design.md) | — | ready to start |
 | 7 | [metered-licensing](2026-07-26-metered-licensing-design.md) | [plan](../plans/2026-07-26-metered-licensing.md) | **shipped** — staff can configure and issue any of the six plans; no customer can buy one until 5 lands |