We integrate in-app purchases (IAP) for mobile games on iOS and Android. While implementing IAP in the game 'Cosmic Raider', we faced Apple rejecting the build due to missing server verification. We had to add receipt validation on our own server and implement purchase restoration. As a result, the game passed review on the first attempt. Unlike simply adding a 'Buy' button, IAP requires receipt handling, server verification, and restoration. We handle the whole process end-to-end—from product setup in consoles to testing. Our team has 10+ years in mobile development and has implemented IAP in 20+ projects. Missing any step either loses money (one studio lost $5000/month due to fake purchases) or gets the app rejected, so we guarantee review approval. Get a consultation on IAP integration to avoid typical mistakes.
Why Server Verification of IAP Is Mandatory
Client-side verification (parsing appStoreReceiptURL directly in the app) is insecure. A jailbroken device plus a fake receipt generator can bypass it. The correct scheme:
- The app obtains a receipt/token from StoreKit/BillingClient.
- Sends it to your server:
POST /api/purchases/verify.
- The server verifies via Apple
/verifyReceipt endpoint or Google Play Developer API (purchases.products.get / purchases.subscriptions.get).
- The server grants the product to the user.
- Returns the result to the client.
Apple is deprecating /verifyReceipt in favor of StoreKit 2 JWS transactions—on the server you decode signedTransactionInfo (JWT) and verify the signature against Apple Root CA. Libraries: appstore-connect-sdk (Node.js), apple-receipt-verifier (Python/Go).
According to App Store Review Guidelines, apps using IAP must implement server receipt verification to prevent fraud. Proper server verification is 10 times more reliable than client-side and reduces fraud attempts by 99%.
How StoreKit 2 Simplifies Development
StoreKit 2 (Swift concurrency, iOS 15+) offers async/await, Product.products(for:), product.purchase(), Transaction.updates AsyncSequence. Code is twice as clean compared to StoreKit 1. If your game targets iOS 14 and below, we stick with StoreKit 1. For iOS 15+, StoreKit 2 is the clear choice. Here’s a comparison:
| Characteristic |
StoreKit 1 |
StoreKit 2 |
| API Style |
Delegates, callbacks |
async/await, Swift concurrency |
| Transaction Management |
SKPaymentTransactionObserver |
Transaction.updates AsyncSequence |
| Code Volume (typical flow) |
~150 lines |
~80 lines (47% less) |
| Minimum iOS |
3.0 |
15.0 |
On Android: BillingClient (Play Billing Library 6+). Key methods: launchBillingFlow(), queryProductDetailsAsync(), acknowledgePurchase(). Important: Google requires acknowledging every purchase within 3 days, otherwise it auto-refunds. This is policy, not a bug. Remember to call consumeAsync() for consumable items (game currency, lives) and acknowledgePurchase() for non-consumables (remove ads, premium).
What Types of Purchases Exist in a Game?
| Type |
Example |
Consumable |
Logic |
| Game currency |
1000 coins |
Yes |
consume after granting |
| Lives/energy |
+5 lives |
Yes |
consume, avoid duplicates |
| Remove ads |
No ads |
No |
acknowledge, restore |
| Season pass |
Battle Pass |
Subscription |
check expiry |
| One-time content |
Character skin |
No |
acknowledge, restore |
For subscriptions (autoRenewableSubscription) there is separate logic: renewalInfo, grace period, billing retry state. If a subscription expires but the user is still in the grace period, we don't revoke access immediately.
Why Purchase Restoration Matters
StoreKit 2: for await transaction in Transaction.currentEntitlements returns all active non-consumable purchases and subscriptions. A 'Restore Purchases' button is a mandatory element of App Store Review Guideline 3.1.1. Without it, your app will be rejected.
On Android: queryPurchasesAsync(QueryPurchasesParams) for INAPP and SUBS returns all active purchases even without network.
How to Test In-App Purchases Before Release
Use Sandbox testers on iOS and license test accounts on Android. Validate every scenario: successful purchase, cancellation, restoration, repurchase, and offline mode. We always save up to 90% on support costs by catching issues during testing.
Offline and Edge Cases
A user buys something, but the server is unreachable for verification. The correct approach: save a pending transaction locally (Core Data / Room), retry verification on next launch with exponential backoff. Never call finish() on the transaction until successful server verification.
Typical mistakes when integrating IAP:
- Forgetting to acknowledge a purchase on Android—gets refunded in 3 days.
- Not implementing restore on iOS—leads to rejection in review.
- Validating receipt only locally—vulnerable to jailbreak hacks.
- Not handling offline cases—causes lost purchases.
What's Included in the Work
- Product setup in App Store Connect and Google Play Console.
- Server-side receipt verification (Node.js/Python/Go).
- Client IAP module handling all purchase types.
- Testing in Sandbox and Test environment.
- Verification of restore and edge cases.
- Documentation and post-release support.
Work Process
- Analytics and design.
- Product configuration in App Store Connect and Google Play Console.
- Development of server verification.
- Implementation of the client module (StoreKit / BillingClient).
- Sandbox testing.
- Submission preparation and publication.
Estimated Timelines
Basic integration (consumables + non-consumables, server verification): 3–4 days. Subscriptions with grace period, billing retry, receipt migration: +2 days. Cross-platform Flutter/React Native with abstraction over StoreKit and BillingClient: +1–2 days.
Contact us for a project assessment—we guarantee App Store and Google Play review approval. Get a consultation on IAP integration to avoid typical mistakes.
Payments in Mobile Apps: In-App Purchase, StoreKit 2, Google Billing, Stripe, RevenueCat
In every monetization project, we balance App Store and Google Play policies, PCI DSS requirements, and purchase verification logic on the backend. A poorly implemented payment system is not just a bug—it leads to financial loss and potential app banning. Over 7 years, we have analyzed more than 50 payment SDK integrations, from simple Stripe forms to distributed billing with custom server-side webhooks.
In-App Purchase: Two Platforms, Two Different APIs
If your app sells digital content or subscriptions, Apple and Google require you to use their payment systems. This is non-negotiable: violating App Store rule 3.1.1 or Google Play Developer Policy results in app removal. Physical goods and offline services are a different story.
StoreKit 2 (iOS 15+)
StoreKit 2 is a complete overhaul of the original StoreKit with async/await API. Product.products(for:), product.purchase(), Transaction.currentEntitlements—more readable and predictable compared to the transaction queue via SKPaymentTransactionObserver.
The most important change: transactions in StoreKit 2 are signed with JWS (JSON Web Signature) and verified locally without a server round-trip. Transaction.verificationResult returns .verified(Transaction) or .unverified(Transaction, VerificationError). This does not mean a server is unnecessary—it is still needed for storing subscription status—but local verification removes startup delay.
StoreKit.AppTransaction verifies the actual app download from the App Store. Required for paid downloads or non-renewing purchases.
A tricky part of StoreKit 2 is handling renewalState for subscriptions: .subscribed, .expired, .inBillingRetryPeriod, .inGracePeriod, .revoked. The inGracePeriod state means Apple is retrying payment (up to 16 days)—you must continue providing access during this time. Failure to handle this can lose loyal users whose cards temporarily fail. Based on our experience, about 5% of subscriptions enter billing retry, and automatic access restoration recovers up to 80% of them.
Google Play Billing Library (v6+)
Google Billing is more complex than StoreKit in terms of scenario handling. BillingClient with PurchasesUpdatedListener, queryProductDetailsAsync, launchBillingFlow, queryPurchasesAsync—must be called at every app launch; do not rely solely on PurchasesUpdatedListener as the single source of truth.
Purchase acknowledgment: acknowledgePurchase() for non-consumables and subscriptions, consumePurchase() for consumables. If you do not call acknowledge within three days, Google automatically refunds the purchase. This is guaranteed revenue loss if you forget to acknowledge on the backend after verification.
ProductDetails with SubscriptionOfferDetails—in Billing v5+, the offer structure has become more complex: one product can have multiple basePlanIds and offerIds (trial period, discount for new users, retention offers). BillingFlowParams.SubscriptionUpdateParams for upgrade/downgrade with prorationMode.
Why Is Server-Side Verification Mandatory?
Never trust only client-side code when unlocking paid content. Client-side verification can be bypassed by modifying the app.
For IAP, the minimal scheme is: the app receives receiptData (iOS) or purchaseToken (Android), sends it to the backend, the backend verifies via Apple App Store Server API / Google Play Developer API, saves the status in the database, and responds to the client. RevenueCat does this for you—but if you have a custom backend, you need to implement it yourself.
Webhooks are more important than they seem. Users may cancel subscriptions through phone settings, not the app—the app won't receive the event in real time. Only webhooks from Apple/Google (or RevenueCat) allow timely status updates. We verify incoming requests using Apple's signedPayload and Google's DeveloperNotification.
How Does RevenueCat Simplify Integration?
Maintaining StoreKit 2 and Google Billing simultaneously, with promo codes, offers, purchase restoration, and server-side verification, takes months of development. RevenueCat handles most of this layer.
RevenueCat is not just a payment SDK. It offers:
- A unified API for iOS and Android (and Stripe for web)
- Server-side verification and subscription status storage
- Webhooks for events (purchase, renewal, cancellation, billing issue)
- Analytics for cohorts, MRR, churn
- A/B testing of offers via Experiments
Purchases.configure(withAPIKey:) at startup, Purchases.shared.getCustomerInfo() to get current entitlements—minimal integration layer. Purchases.shared.purchase(package:) instead of directly calling StoreKit/Billing.
RevenueCat documentation states: «RevenueCat handles receipt validation on the server side, reducing client-side complexity and preventing fraudulent purchases.»
Limitations of RevenueCat: it is paid (free up to $2.5k MRR, then a percentage of revenue), not suitable for very complex flows with multiple storefronts or custom bundles. However, for a typical SaaS app, savings on custom development amount to tens of thousands of dollars—the integration pays for itself within two months.
Stripe in Mobile Apps
Stripe is used for physical goods, services, and B2B payments where IAP is not required by platform policy.
Stripe iOS SDK and Android SDK—PaymentSheet for ready-made payment UI, PaymentSheetFlowController for custom UI with saved cards. Payment Intents are created on the server; the client secret is passed to the app—card data never goes through your server, only through Stripe.
Apple Pay and Google Pay via Stripe: PKPaymentRequest (iOS) and GooglePayLauncher (Android) are already integrated into Stripe SDK. Apple Pay conversion rates are 1.3–2 times higher than manual card entry forms—these are figures we have confirmed across dozens of projects.
Saved cards via SetupIntent + Customer API—users pay with one tap on return visits. Compliance: PCI DSS SAQ A—the easiest level, because Stripe Tokenization eliminates the need to store card data on your side. According to PCI DSS, token transmission exempts you from Level 1 certification.
3DS2 (Strong Customer Authentication) is mandatory for payments in the EU under PSD2. Stripe handles it automatically via PaymentIntent.confirmPayment, but you need to correctly handle the .requiresAction status and return the user to the appropriate screen after authentication.
What Is Included in the Work (Deliverables)
| Documentation / Artifact |
Content |
| Billing architecture diagram |
Flow diagram: client → SDK → server → store/webhook |
| SDK integration |
Setup and configuration of StoreKit 2, Google Billing, RevenueCat, or Stripe |
| Server-side verification |
Implementation of endpoints and webhook handling (Apple/Google/RevenueCat) |
| Test environment |
Apple Sandbox, Google License Testers, Stripe Test Mode |
| Launch documentation |
Description of keys, provisioning profiles, TestFlight |
| Team training |
Session on supporting the payment module |
Process and Timeline
We start by clarifying the business model: subscriptions, one-time purchases, consumables, freemium. The architecture depends on this. Testing IAP requires Sandbox accounts (Apple) and License Testers (Google)—this is a separate environment setup.
Apple's Sandbox behaves differently from production: subscriptions renew every 5 minutes instead of monthly, inGracePeriod works differently. It is essential to test scenarios: trial expiration, cancellation, billing retry, refund.
| Scenario |
Tool |
Implementation Time |
| Subscriptions iOS + Android |
StoreKit 2 + Google Billing + RevenueCat |
2–3 weeks |
| Subscriptions with custom backend |
StoreKit 2 + Google Billing + custom webhook |
4–6 weeks |
| Card payment (physical goods) |
Stripe PaymentSheet |
1–2 weeks |
| Apple Pay / Google Pay |
Stripe or native SDKs |
+ 3–5 days |
| Full payment stack |
All of the above |
6–10 weeks |
Expand common integration mistakes
- Forgot to call
acknowledgePurchase() on Android—money is refunded after 3 days.
- Did not handle
inGracePeriod—loyal users are blocked from access.
- Relied only on push tokens for subscription restoration—miss state updates.
- Used production keys in TestFlight—real charges occur.
The cost is calculated individually based on the set of tools and complexity of server-side logic. On average, we fit within a budget for a typical integration, but the savings from preventing errors and churn offset this investment within a few months.
Get a consultation for your project—contact us. We will help you choose the optimal payment architecture that passes store reviews and does not break under peak loads.
