Cross-platform entitlement sync if app is on both stores

A user who subscribes on iOS, reinstalls on Android, and discovers their subscription is not recognized will either double-pay or churn. Validating Apple receipts into one database table and Google purchase tokens into another with no shared user_id link splits a single paying customer into two half-customers — and the data-integrity hit compounds when refunds, cancellations, or plan changes arrive on one platform but never reach the other. Cross-platform sync is a churn and support-load problem, not a store policy one.

Configure both iOS and Android apps under a single RevenueCat (or Adapty/Qonversion) project using the same entitlement identifiers — the SDK then resolves entitlements against a unified customer profile automatically. For a custom backend, have both api/validate-apple.ts and api/validate-google.ts write to a single user_entitlements table keyed by your internal user_id, not by the platform-native purchase identifier, so a logged-in user sees the same is_premium = true on either device.