Axiom In App Purchases

StoreKit 2 In-App Purchase Implementation

Purpose: Guide robust, testable in-app purchase implementation StoreKit Version: StoreKit 2 iOS Version: iOS 15+ (iOS 18.4+ for latest features) Xcode: Xcode 13+ (Xcode 16+ recommended) Context: WWDC 2025-241, 2025-249, 2023-10013, 2021-10114

When to Use This Skill

✅ Use this skill when:

• Implementing any in-app purchase functionality (new or existing)
• Adding consumable products (coins, hints, boosts)
• Adding non-consumable products (premium features, level packs)
• Adding auto-renewable subscriptions (monthly/annual plans)
• Debugging purchase failures, missing transactions, or restore issues
• Setting up StoreKit testing configuration
• Implementing subscription status tracking
• Adding promotional offers or introductory offers
• Server-side receipt validation
• Family Sharing support

❌ Do NOT use this skill for:

• StoreKit 1 (legacy API) - this skill focuses on StoreKit 2
• App Store Connect product configuration (separate documentation)
• Pricing strategy or business model decisions

⚠️ Already Wrote Code Before Creating .storekit Config?

If you wrote purchase code before creating .storekit configuration, you have three options:

Option A: Delete and Start Over (Strongly Recommended)

Delete all IAP code and follow the testing-first workflow below. This reinforces correct habits and ensures you experience the full benefit of .storekit-first development.

Why this is best:

• Validates that you understand the workflow
• Catches product ID issues you might have missed
• Builds muscle memory for future IAP implementations
• Takes only 15-30 minutes for experienced developers

Option B: Create .storekit Config Now (Acceptable with Caution)

Create the .storekit file now with your existing product IDs. Test everything works locally. Document in your PR that you tested in sandbox first.

Trade-offs:

• ✅ Keeps working code
• ✅ Adds local testing capability
• ❌ Misses product ID validation benefit
• ❌ Reinforces testing-after pattern
• ❌ Requires extra vigilance in code review

If choosing this path: Create .storekit immediately, verify locally, and commit a note explaining the approach.

Option C: Skip .storekit Entirely (Not Recommended)

Commit without .storekit configuration, test only in sandbox.

Why this is problematic:

• Teammates can't test purchases locally
• No validation of product IDs before runtime
• Harder iteration (requires App Store Connect)
• Missing documentation of product structure

Bottom line: Choose Option A if possible, Option B if pragmatic, never Option C.

Core Philosophy: Testing-First Workflow

Best Practice: Create and test StoreKit configuration BEFORE writing production purchase code.

Why .storekit-First Matters

The recommended workflow is to create .storekit configuration before writing any purchase code. This isn't arbitrary - it provides concrete benefits:

Immediate product ID validation:

• Typos caught in Xcode, not at runtime
• Product configuration visible in project
• No App Store Connect dependency for testing

Faster iteration:

• Test purchases in simulator instantly
• No network requests during development
• Accelerated subscription renewal for testing

Team benefits:

• Anyone can test purchase flows locally
• Product catalog documented in code
• Code review includes purchase testing

Common objections addressed:

❓ "I already tested in sandbox" - Sandbox testing is valuable but comes later. Local testing with .storekit is faster and enables true TDD.

❓ "My code works" - Working code is great! Adding .storekit makes it easier for teammates to verify and maintain.

❓ "I've done this before" - Experience is valuable. The .storekit-first workflow makes experienced developers even more productive.

❓ "Time pressure" - Creating .storekit takes 10-15 minutes. The time saved in iteration pays back immediately.

The Recommended Workflow

StoreKit Config → Local Testing → Production Code → Unit Tests → Sandbox Testing
      ↓               ↓                ↓               ↓              ↓
   .storekit      Test purchases   StoreManager    Mock store    Integration test

Why this order helps:

1. StoreKit Config First: Defines products without App Store Connect dependency
2. Local Testing: Validates product IDs and purchase flows immediately
3. Production Code: Implements against validated product configuration
4. Unit Tests: Verifies business logic with mocked store responses
5. Sandbox Testing: Final validation in App Store environment

Benefits of following this workflow:

• Product IDs validated before writing code
• Faster development iteration
• Easier team collaboration
• Better test coverage

Mandatory Checklist

Before marking IAP implementation complete, ALL items must be verified:

Phase 1: Testing Foundation

• Created .storekit configuration file with all products
• Verified each product type renders correctly in StoreKit preview
• Tested successful purchase flow for each product in Xcode
• Tested purchase failure scenarios (insufficient funds, cancelled)
• Tested restore purchases flow
• For subscriptions: tested renewal, expiration, and upgrade/downgrade

Phase 2: Architecture

• Centralized StoreManager class exists (single source of truth)
• StoreManager is ObservableObject (SwiftUI) or uses NotificationCenter
• Transaction observer listens for updates via Transaction.updates
• All transaction verification uses VerificationResult
• All transactions call .finish() after entitlement granted
• Product loading happens at app launch or before displaying store

Phase 3: Purchase Flow

• Purchase uses new purchase(confirmIn:options:) with UI context (iOS 18.2+)
• Purchase handles all PurchaseResult cases (success, userCancelled, pending)
• Purchase verifies transaction signature before granting entitlement
• Purchase stores transaction receipt/identifier for support
• appAccountToken set for all purchases (if using server backend)

Phase 4: Subscription Management (if applicable)

• Subscription status tracked via Product.SubscriptionInfo.Status
• Current entitlements checked via Transaction.currentEntitlements(for:)
• Renewal info accessed for expiration, renewal date, offer status
• Subscription views use ProductView or SubscriptionStoreView
• Win-back offers implemented for expired subscriptions
• Grace period and billing retry states handled

Phase 5: Restore & Sync

• Restore purchases implemented (required by App Store Review)
• Restore uses Transaction.currentEntitlements or Transaction.all
• Family Sharing transactions identified (if supported)
• Server sync implemented (if using backend)
• Cross-device entitlement sync tested

Phase 6: Error Handling

• Network errors handled gracefully (retries, user messaging)
• Invalid product IDs detected and logged
• Purchase failures show user-friendly error messages
• Transaction verification failures logged and reported
• Refund notifications handled (via App Store Server Notifications)

Phase 7: Testing & Validation

• Unit tests verify purchase logic with mocked Product/Transaction
• Unit tests verify subscription status determination
• Integration tests with StoreKit configuration pass
• Sandbox testing with real Apple ID completed
• TestFlight testing completed before production release

Step 1: Create StoreKit Configuration (FIRST!)

DO THIS BEFORE WRITING ANY PURCHASE CODE.

Create Configuration File

1. Xcode → File → New → File → StoreKit Configuration File
2. Save as: Products.storekit (or your app name)
3. Add to target: ✅ (include in app bundle for testing)

Add Products

Click "+" and add each product type:

Consumable

Product ID: com.yourapp.coins_100
Reference Name: 100 Coins
Price: $0.99

Non-Consumable

Product ID: com.yourapp.premium
Reference Name: Premium Upgrade
Price: $4.99

Auto-Renewable Subscription

Product ID: com.yourapp.pro_monthly
Reference Name: Pro Monthly
Price: $9.99/month
Subscription Group ID: pro_tier

Test Immediately

1. Run app in simulator
2. Scheme → Edit Scheme → Run → Options
3. StoreKit Configuration: Select Products.storekit
4. Verify: Products load, purchases complete, transactions appear

Step 2: Implement StoreManager Architecture

Required Pattern: Centralized StoreManager

All purchase logic must go through a single StoreManager. No scattered Product.purchase() calls throughout app.

import StoreKit

@MainActor
final class StoreManager: ObservableObject {
    // Published state for UI
    @Published private(set) var products: [Product] = []
    @Published private(set) var purchasedProductIDs: Set<String> = []

    // Product IDs from StoreKit configuration
    private let productIDs = [
        "com.yourapp.coins_100",
        "com.yourapp.premium",
        "com.yourapp.pro_monthly"
    ]

    private var transactionListener: Task<Void, Never>?

    init() {
        // Start transaction listener immediately
        transactionListener = listenForTransactions()

        Task {
            await loadProducts()
            await updatePurchasedProducts()
        }
    }

    deinit {
        transactionListener?.cancel()
    }
}

Why @MainActor: Published properties must update on main thread for UI binding.

Load Products (At Launch)

extension StoreManager {
    func loadProducts() async {
        do {
            // Load products from App Store
            let loadedProducts = try await Product.products(for: productIDs)

            // Update published property on main thread
            self.products = loadedProducts

        } catch {
            print("Failed to load products: \(error)")
            // Show error to user
        }
    }
}

Call from: App.init() or first view's .task modifier

Listen for Transactions (REQUIRED)

extension StoreManager {
    func listenForTransactions() -> Task<Void, Never> {
        Task.detached { [weak self] in
            // Listen for ALL transaction updates
            for await verificationResult in Transaction.updates {
                await self?.handleTransaction(verificationResult)
            }
        }
    }

    @MainActor
    private func handleTransaction(_ result: VerificationResult<Transaction>) async {
        // Verify transaction signature
        guard let transaction = try? result.payloadValue else {
            print("Transaction verification failed")
            return
        }

        // Grant entitlement to user
        await grantEntitlement(for: transaction)

        // CRITICAL: Always finish transaction
        await transaction.finish()

        // Update purchased products
        await updatePurchasedProducts()
    }
}

Why detached: Transaction listener runs independently of view lifecycle

Step 3: Implement Purchase Flow

Purchase with UI Context (iOS 18.2+)

extension StoreManager {
    func purchase(_ product: Product, confirmIn scene: UIWindowScene) async throws -> Bool {
        // Perform purchase with UI context for payment sheet
        let result = try await product.purchase(confirmIn: scene)

        switch result {
        case .success(let verificationResult):
            // Verify the transaction
            guard let transaction = try? verificationResult.payloadValue else {
                print("Transaction verification failed")
                return false
            }

            // Grant entitlement
            await grantEntitlement(for: transaction)

            // CRITICAL: Finish transaction
            await transaction.finish()

            // Update state
            await updatePurchasedProducts()

            return true

        case .userCancelled:
            // User tapped "Cancel" in payment sheet
            return false

        case .pending:
            // Purchase requires action (Ask to Buy, payment issue)
            // Will be delivered via Transaction.updates when approved
            return false

        @unknown default:
            return false
        }
    }
}

SwiftUI Purchase (Using Environment)

struct ProductRow: View {
    let product: Product
    @Environment(\.purchase) private var purchase

    var body: some View {
        Button("Buy \(product.displayPrice)") {
            Task {
                do {
                    let result = try await purchase(product)
                    // Handle result
                } catch {
                    print("Purchase failed: \(error)")
                }
            }
        }
    }
}

Set appAccountToken (If Using Backend)

func purchase(
    _ product: Product,
    confirmIn scene: UIWindowScene,
    accountToken: UUID
) async throws -> Bool {
    // Purchase with appAccountToken for server-side association
    let result = try await product.purchase(
        confirmIn: scene,
        options: [
            .appAccountToken(accountToken)
        ]
    )

    // ... handle result
}

When to use: When your backend needs to associate purchases with user accounts

Step 4: Verify Transactions (MANDATORY)

Always Use VerificationResult

func handleTransaction(_ result: VerificationResult<Transaction>) async {
    switch result {
    case .verified(let transaction):
        // ✅ Transaction signed by App Store
        await grantEntitlement(for: transaction)
        await transaction.finish()

    case .unverified(let transaction, let error):
        // ❌ Transaction signature invalid
        print("Unverified transaction: \(error)")
        // DO NOT grant entitlement
        // DO finish transaction to clear from queue
        await transaction.finish()
    }
}

Why verify: Prevents granting entitlements for:

• Fraudulent receipts
• Jailbroken device receipts
• Man-in-the-middle attacks

Check Transaction Fields

func grantEntitlement(for transaction: Transaction) async {
    // Check transaction hasn't been revoked
    guard transaction.revocationDate == nil else {
        print("Transaction was refunded")
        await revokeEntitlement(for: transaction.productID)
        return
    }

    // Grant based on product type
    switch transaction.productType {
    case .consumable:
        await addConsumable(productID: transaction.productID)

    case .nonConsumable:
        await unlockFeature(productID: transaction.productID)

    case .autoRenewable:
        await activateSubscription(productID: transaction.productID)

    default:
        break
    }
}

Step 5: Track Current Entitlements

Check What User Owns

extension StoreManager {
    func updatePurchasedProducts() async {
        var purchased: Set<String> = []

        // Iterate through all current entitlements
        for await result in Transaction.currentEntitlements {
            guard let transaction = try? result.payloadValue else {
                continue
            }

            // Only include active entitlements (not revoked)
            if transaction.revocationDate == nil {
                purchased.insert(transaction.productID)
            }
        }

        self.purchasedProductIDs = purchased
    }
}

Check Specific Product

func isEntitled(to productID: String) async -> Bool {
    // Check current entitlements for specific product
    for await result in Transaction.currentEntitlements(for: productID) {
        if let transaction = try? result.payloadValue,
           transaction.revocationDate == nil {
            return true
        }
    }

    return false
}

Step 6: Implement Subscription Management

Track Subscription Status

extension StoreManager {
    func checkSubscriptionStatus(for groupID: String) async -> Product.SubscriptionInfo.Status? {
        // Get subscription statuses for group
        guard let result = try? await Product.SubscriptionInfo.status(for: groupID),
              let status = result.first else {
            return nil
        }

        return status.state
    }
}

Handle Subscription States

func updateSubscriptionUI(for status: Product.SubscriptionInfo.Status) {
    switch status.state {
    case .subscribed:
        // User has active subscription
        showSubscribedContent()

    case .expired:
        // Subscription expired - show win-back offer
        showResubscribeOffer()

    case .inGracePeriod:
        // Billing issue - show payment update prompt
        showUpdatePaymentPrompt()

    case .inBillingRetryPeriod:
        // Apple retrying payment - maintain access
        showBillingRetryMessage()

    case .revoked:
        // Family Sharing access removed
        removeAccess()

    @unknown default:
        break
    }
}

Use StoreKit Views (iOS 17+)

struct SubscriptionView: View {
    var body: some View {
        SubscriptionStoreView(groupID: "pro_tier") {
            // Marketing content
            VStack {
                Image("premium-icon")
                Text("Unlock all features")
            }
        }
        .subscriptionStoreControlStyle(.prominentPicker)
    }
}

Step 7: Implement Restore Purchases (REQUIRED)

Restore Flow

extension StoreManager {
    func restorePurchases() async {
        // Sync all transactions from App Store
        try? await AppStore.sync()

        // Update current entitlements
        await updatePurchasedProducts()
    }
}

UI Button

struct SettingsView: View {
    @StateObject private var store = StoreManager()

    var body: some View {
        Button("Restore Purchases") {
            Task {
                await store.restorePurchases()
            }
        }
    }
}

App Store Requirement: Apps with IAP must provide restore functionality for non-consumables and subscriptions.

Step 8: Handle Refunds

Listen for Refund Notifications

extension StoreManager {
    func listenForTransactions() -> Task<Void, Never> {
        Task.detached { [weak self] in
            for await verificationResult in Transaction.updates {
                await self?.handleTransaction(verificationResult)
            }
        }
    }

    @MainActor
    private func handleTransaction(_ result: VerificationResult<Transaction>) async {
        guard let transaction = try? result.payloadValue else {
            return
        }

        // Check if transaction was refunded
        if let revocationDate = transaction.revocationDate {
            print("Transaction refunded on \(revocationDate)")
            await revokeEntitlement(for: transaction.productID)
        } else {
            await grantEntitlement(for: transaction)
        }

        await transaction.finish()
    }
}

Step 9: Unit Testing

Mock Store Responses

protocol StoreProtocol {
    func products(for ids: [String]) async throws -> [Product]
    func purchase(_ product: Product) async throws -> PurchaseResult
}

// Production
final class StoreManager: StoreProtocol {
    func products(for ids: [String]) async throws -> [Product] {
        try await Product.products(for: ids)
    }
}

// Testing
final class MockStore: StoreProtocol {
    var mockProducts: [Product] = []
    var mockPurchaseResult: PurchaseResult?

    func products(for ids: [String]) async throws -> [Product] {
        mockProducts
    }

    func purchase(_ product: Product) async throws -> PurchaseResult {
        mockPurchaseResult ?? .userCancelled
    }
}

Test Purchase Logic

@Test func testSuccessfulPurchase() async {
    let mockStore = MockStore()
    let manager = StoreManager(store: mockStore)

    // Given: Mock successful purchase
    mockStore.mockPurchaseResult = .success(.verified(mockTransaction))

    // When: Purchase product
    let result = await manager.purchase(mockProduct)

    // Then: Entitlement granted
    #expect(result == true)
    #expect(manager.purchasedProductIDs.contains("com.app.premium"))
}

@Test func testCancelledPurchase() async {
    let mockStore = MockStore()
    let manager = StoreManager(store: mockStore)

    // Given: User cancels
    mockStore.mockPurchaseResult = .userCancelled

    // When: Purchase product
    let result = await manager.purchase(mockProduct)

    // Then: No entitlement granted
    #expect(result == false)
    #expect(manager.purchasedProductIDs.isEmpty)
}

Common Anti-Patterns (NEVER DO THIS)

❌ No StoreKit Configuration

// ❌ WRONG: Writing purchase code without .storekit file
let products = try await Product.products(for: productIDs)
// Can't test this without App Store Connect setup!

✅ Correct: Create .storekit file FIRST, test in Xcode, THEN implement.

❌ Code Before .storekit Config

// ❌ Less ideal: Write code, test in sandbox, add .storekit later
let products = try await Product.products(for: productIDs)
let result = try await product.purchase(confirmIn: scene)
// "I tested this in sandbox, it works! I'll add .storekit config later."

✅ Recommended: Create .storekit config first, then write code.

If you're in this situation: See "Already Wrote Code Before Creating .storekit Config?" section above for your options (A, B, or C).

Why .storekit-first is better:

• Product ID typos caught in Xcode, not at runtime
• Faster iteration without network requests
• Teammates can test locally
• Documents product structure in code

Sandbox testing is valuable - it validates against real App Store infrastructure. But starting with .storekit makes sandbox testing easier because you've already validated product IDs locally.

❌ Scattered Purchase Calls

// ❌ WRONG: Purchase calls scattered throughout app
Button("Buy") {
    try await product.purchase()  // In view 1
}

Button("Subscribe") {
    try await subscriptionProduct.purchase()  // In view 2
}

✅ Correct: All purchases through centralized StoreManager.

❌ Forgetting to Finish Transactions

// ❌ WRONG: Never calling finish()
func handleTransaction(_ transaction: Transaction) {
    grantEntitlement(for: transaction)
    // Missing: await transaction.finish()
}

✅ Correct: ALWAYS call transaction.finish() after granting entitlement.

❌ Not Verifying Transactions

// ❌ WRONG: Using unverified transaction
for await transaction in Transaction.all {
    grantEntitlement(for: transaction)  // Unsafe!
}

✅ Correct: Always check VerificationResult before granting.

❌ Ignoring Transaction Listener

// ❌ WRONG: Only handling purchases in purchase() method
func purchase() {
    let result = try await product.purchase()
    // What about pending purchases, family sharing, restore?
}

✅ Correct: Listen to Transaction.updates for ALL transaction sources.

❌ Not Implementing Restore

// ❌ WRONG: No restore button
// App Store will REJECT your app!

✅ Correct: Provide visible "Restore Purchases" button in settings.

Validation

Before marking IAP implementation complete, verify:

Code Inspection

Run these searches to verify compliance:

# Check StoreKit configuration exists
find . -name "*.storekit"

# Check transaction.finish() is called
rg "transaction\.finish\(\)" --type swift

# Check VerificationResult usage
rg "VerificationResult" --type swift

# Check Transaction.updates listener
rg "Transaction\.updates" --type swift

# Check restore implementation
rg "AppStore\.sync|Transaction\.all" --type swift

Functional Testing

• Can purchase each product type in StoreKit configuration
• Can cancel purchase and state remains consistent
• Can restore purchases and regain access
• Subscription renewal/expiration works as expected
• Refunded transactions revoke access
• Family Sharing transactions identified (if supported)

Sandbox Testing

• Real Apple ID sandbox purchases complete
• TestFlight beta testers confirm purchase flows work
• Server-side validation works (if using backend)

App Store Connect Submission (see app-store-submission for full checklist)

• Review screenshot uploaded for each IAP product (shows purchase UI — review-only, not on App Store)
• IAP products attached to this version (first submission: App Version → In-App Purchases section → Select → checkbox each product)
• Terms of Use + Privacy Policy links on purchase screen (required by DPLA Schedule 2; SubscriptionStoreView handles this automatically)
• Subscription terms explicit: price, period, auto-renewal, cancellation

Resources

WWDC: 2025-241, 2025-249, 2023-10013, 2021-10114

Docs: /storekit, /appstoreserverapi

Skills: axiom-storekit-ref

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