rc-backend - SKILL.md Agent Skill

name: rc-backend description: Use this skill when your backend needs to read or update RevenueCat state on Android. Covers the RevenueCat REST API (v1 subscribers endpoint, grant/revoke entitlements, attributes), secret vs public SDK API key usage, and why you do not build a receipt verification backend with RevenueCat. license: Apache-2.0; see LICENSE metadata: author: RevenueCat source: revenuecat-handbook chapter 9 keywords: - android - revenuecat - backend - rest-api - entitlement-grant - secret-api-key

Backend Architecture with RevenueCat

You do not build a receipt verification server with RevenueCat. Your backend still has a role, but that role is consuming RevenueCat state, not validating Google Play purchase tokens.

Phase 1: Discovery

RevenueCat's backend is the receipt verification server. When the Android SDK posts a purchase token, RevenueCat's backend:

Calls purchases.subscriptionsv2.get or purchases.products.get against the Google Play Developer API.
Validates the receipt is genuine and matches the expected product.
Records the transaction in its database.
Returns CustomerInfo to the SDK.

Your Android app never calls the Google Play Developer API. Your server does not call it either.

Before writing any backend code, confirm these facts about your deployment:

You have a RevenueCat project with an Android app configured.
You have a secret API key from Project Settings to API Keys (not the public Android SDK key embedded in the app).
You know which app_user_id your SDK uses (the same identifier your auth system uses).
You have decided whether the backend needs real time state (REST API) or event driven state (webhooks).

If your app only gates features inside the client, you may not need a backend component at all. RevenueCat verifies CustomerInfo server side before it reaches the SDK, and EntitlementVerificationMode.INFORMATIONAL or .ENFORCED adds signature verification on the client. Serve premium content from a server only when you can verify entitlement on the server.

Phase 2: Plan

Map each backend responsibility to a RevenueCat mechanism.

Use case	Mechanism	Notes
React to purchase, renewal, cancellation	Webhook receiver	RevenueCat posts normalized events; your server updates its own DB.
Check current entitlement for a user	`GET /v1/subscribers/{app_user_id}`	Secret API key in `Authorization` header.
Grant promotional access (support, refunds, comps)	`POST /v1/subscribers/{app_user_id}/entitlements/{entitlement_id}/promotional`	Server side only.
Revoke promotional access	`POST /v1/subscribers/{app_user_id}/entitlements/{entitlement_id}/revoke_promotionals`	Server side only.
Set subscriber attributes from server side data	`POST /v1/subscribers/{app_user_id}/attributes`	Useful for CRM fields the SDK does not know.
Bulk data export	RevenueCat data export	Scheduled exports to your warehouse.

What your backend still owns:

User authentication.
Your database of users and their access levels.
API endpoints that serve premium content.
The webhook receiver that processes RevenueCat events.

What your backend does not own:

Google Play Developer API credentials.
Receipt verification code.
linkedPurchaseToken chain traversal.
Subscription state computation across the seven subscription states.

Phase 3: Execute

Read a subscriber

GET https://api.revenuecat.com/v1/subscribers/{app_user_id}
Authorization: Bearer sk_...
X-Platform: android

The response body is the same CustomerInfo structure the Android SDK returns. Use it in a server side endpoint that gates premium API responses.

Grant a promotional entitlement

POST https://api.revenuecat.com/v1/subscribers/{app_user_id}/entitlements/{entitlement_id}/promotional
Authorization: Bearer sk_...
Content-Type: application/json

{"duration": "monthly"}

Valid duration values include daily, three_day, weekly, monthly, two_month, three_month, six_month, yearly, lifetime. Use this for support workflows, never from the client.

Example: Kotlin Ktor call from your server

val response = client.get("https://api.revenuecat.com/v1/subscribers/$appUserId") {
    header("Authorization", "Bearer ${System.getenv("RC_SECRET_KEY")}")
    header("X-Platform", "android")
}

API key rules

Key	Where it lives	What it can do
Android public SDK key	Embedded in the Android app	Post purchases, fetch `CustomerInfo` for the current user.
Secret API key	Server environment variable only	Read any subscriber, grant or revoke promotionals, set attributes, bulk operations.

Never ship the secret key in the Android APK, in a BuildConfig field, or in any client bundle. Rotate it if it leaks. Treat it like a database password.

Webhook receiver outline

post("/revenuecat/webhook") {
    val auth = call.request.header("Authorization")
    require(auth == "Bearer ${System.getenv("RC_WEBHOOK_SECRET")}")
    val event = call.receive<RevenueCatEvent>()
    when (event.type) {
        "INITIAL_PURCHASE", "RENEWAL" -> grantAccess(event.appUserId, event.entitlements)
        "CANCELLATION", "EXPIRATION" -> scheduleRevocation(event.appUserId)
    }
    call.respond(HttpStatusCode.OK)
}

Verify the authorization header you configured in the RevenueCat dashboard. Respond 2xx fast; RevenueCat retries on non 2xx responses.

What not to build

Do not build a Google Play receipt verification endpoint. RevenueCat already did.
Do not pass purchase tokens from the Android client to your server for manual verification. The SDK handles the round trip.
Do not query Google Play Developer API from your backend unless you are building a custom integration that bypasses the SDK.
Do not mirror the seven subscription state machine in your DB. Consume CustomerInfo.entitlements.active or webhook events instead.

References

Full chapter