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Version: 1.0-rc

Frequently Asked Questions

IAPKit - In-App Purchase Made Simple

Common questions and answers about kmp-iap.

General Questions​

Q: What platforms does kmp-iap support?​

A: The library supports:

  • iOS: 15.0+ with StoreKit 2
  • Android: API 21+ (Android 5.0) with Google Play Billing Library v7+
  • Desktop & Web: Planned for future releases

Windows, Linux, and Web support is on the roadmap as Kotlin Multiplatform expands to these platforms.

Q: How is kmp-iap different from flutter_inapp_purchase?​

A: Key differences:

  • Technology: kmp-iap uses Kotlin Multiplatform vs Flutter/Dart
  • State Management: StateFlow vs Streams
  • Integration: Works with Compose Multiplatform, native Android/iOS
  • API Design: Coroutines-based vs Future/async-await

Q: Is this library free to use?​

A: Yes, kmp-iap is open source and free to use under the MIT license. However, both Apple and Google charge fees for in-app purchases (typically 15-30%).

Setup & Configuration​

Q: Do I need to configure anything in Xcode or Android Studio?​

A: Yes, minimal setup is required:

iOS:

  • Enable In-App Purchase capability in Xcode
  • Configure products in App Store Connect

Android:

  • Add <uses-permission android:name="com.android.vending.BILLING" /> to AndroidManifest.xml
  • Configure products in Google Play Console

See our setup guides for detailed instructions.

Q: Can I test purchases without publishing my app?​

A: Yes:

iOS: Use sandbox testing with sandbox Apple IDs Android: Upload to Internal Testing track in Play Console

Both platforms require proper store setup but don't require public app release.

Q: How long does it take for products to appear after configuration?​

A: Product availability varies:

  • iOS: Usually within a few hours, up to 24 hours
  • Android: Can take 24-48 hours after app upload

Products must be properly configured and approved in the respective stores.

Products & Subscriptions​

Q: What's the difference between consumable and non-consumable products?​

A:

  • Consumable: Can be purchased multiple times (coins, gems, power-ups)
  • Non-consumable: Purchased once, owned forever (remove ads, premium features)
  • Subscriptions: Recurring purchases with auto-renewal

Q: How do I handle different product types?​

A: Use the isConsumable parameter:

// For consumable products
val success = kmpIapInstance.finishTransaction(
    purchase = purchase.toPurchaseInput(),
    isConsumable = true
)

// For non-consumable products and subscriptions
val success = kmpIapInstance.finishTransaction(
    purchase = purchase.toPurchaseInput(),
    isConsumable = false
)

Q: Can I offer subscription trials?​

A: Yes, but setup varies by platform:

  • iOS: Configure introductory offers in App Store Connect
  • Android: Configure free trials in Play Console

The library will return trial information in the product data.

Q: How do I handle subscription renewals?​

A: Subscriptions auto-renew by default. To check status:

scope.launch {
    val purchases = kmpIapInstance.getAvailablePurchases()
        val activeSubscriptions = purchases.filter { purchase ->
            subscriptionIds.contains(purchase.productId) &&
            isActive(purchase)
        }
    }
}

Implement server-side receipt validation for accurate expiration checking.

Purchases & Transactions​

Q: Why isn't my purchase completing?​

A: Common causes:

  1. Not finishing transactions: Always call finishTransaction()
  2. No state observers: Set up StateFlow collectors before requesting purchases
  3. Network issues: Ensure device has internet connectivity
  4. Account issues: Verify store account is properly set up

Q: How do I restore purchases?​

A: Purchases are automatically available via StateFlow:

suspend fun restorePurchases() {
    try {
        // Get available purchases
        val purchases = kmpIapInstance.getAvailablePurchases()
        purchases.forEach { purchase ->
            // Re-deliver non-consumable products
            if (isNonConsumable(purchase.productId)) {
                deliverProduct(purchase)
            }
        }
    } catch (e: PurchaseError) {
        println("Restore failed: $e")
    }
}

Q: Can users purchase the same product multiple times?​

A: Depends on product type:

  • Consumable: Yes, after finishing transaction as consumable
  • Non-consumable: No, will get PRODUCT_ALREADY_OWNED error
  • Subscription: Can upgrade/downgrade, but not duplicate

Q: How do I handle pending purchases on Android?​

A: Monitor purchase state:

private fun handlePurchase(purchase: Purchase) {
    when (purchase.purchaseState) {
        PurchaseState.PURCHASED -> {
            // Purchase completed
            deliverProduct(purchase)
        }
        PurchaseState.PENDING -> {
            // Purchase pending - show pending UI
            showPendingMessage()
        }
    }
}

Security & Validation​

Q: Do I need to validate receipts?​

A: Yes, for production apps you should always validate receipts server-side to prevent fraud. The library provides receipt data, but validation must be implemented separately.

Q: How do I validate iOS receipts?​

A: Send receipt to Apple's verification servers:

// Get receipt data
val receipt = purchase.transactionReceipt

// Send to your server for validation with Apple
val isValid = api.validateIOSReceipt(
    receipt = receipt,
    sharedSecret = "your-shared-secret"
)

Q: How do I validate Android purchases?​

A: Use the purchase token with Google Play Developer API:

// Get purchase token
val token = purchase.purchaseToken

// Validate on your server using Google Play Developer API
val isValid = api.validateAndroidPurchase(
    token = token,
    productId = purchase.productId
)

Q: Can I trust client-side purchase data?​

A: No, never trust client-side data for security-critical operations. Always validate receipts server-side before granting paid content.

Error Handling​

Q: What does "Billing is unavailable" mean?​

A: This indicates the billing system isn't ready. Common causes:

  • Google Play Store not installed/updated (Android)
  • App not uploaded to store (Android)
  • Network connectivity issues
  • Store service temporarily unavailable

Q: Why do I get "Product not found" errors?​

A: Product ID mismatches are common:

  • Verify exact product ID spelling
  • Check product is active in store console
  • Wait for product propagation (up to 24 hours)
  • Ensure app bundle ID matches store configuration

Q: How do I handle purchase cancellations?​

A: Monitor error state:

scope.launch {
    kmpIapInstance.purchaseErrorListener.collect { error ->
        when (error.code) {
            ErrorCode.UserCancelled -> {
                // User cancelled - no error message needed
            }
            else -> {
                // Show error message
                showErrorDialog(error.message)
            }
        }
        // No need to clear error with new API
    }
}

Development & Testing​

Q: Can I test purchases on simulators/emulators?​

A:

  • iOS Simulator: Limited support, use StoreKit testing
  • Android Emulator: Not recommended, use real devices
  • Best practice: Always test on real devices with test accounts

Q: How do I test subscriptions?​

A: Both platforms offer accelerated testing:

  • iOS: Subscriptions renew every few minutes in sandbox
  • Android: Test subscriptions renew quickly in test environment

Q: Do test purchases cost real money?​

A: No:

  • iOS: Sandbox purchases are free
  • Android: License tester purchases are free and auto-refund

Q: How do I clear test purchase history?​

A:

  • iOS: Settings > App Store > Sandbox Account > Reset
  • Android: Google Play Store > Account > Purchase history (cancel test purchases)

Performance & Best Practices​

Q: When should I initialize the IAP connection?​

A: Initialize as early as possible, typically in your ViewModel initialization. Don't initialize on every screen.

Q: How do I handle app lifecycle events?​

A: Clean up properly:

class PurchaseViewModel : ViewModel() {
    init {
        viewModelScope.launch {
            kmpIapInstance.initConnection()
        }
    }

    override fun onCleared() {
        super.onCleared()
        kmpIapInstance.endConnection()
    }
}

Kotlin Multiplatform Specific​

Q: Can I use kmp-iap with SwiftUI?​

A: Yes, the library works with SwiftUI through Kotlin/Native interop:

// In your SwiftUI view
let iapManager = IAPManager() // Your KMP wrapper

Button("Purchase") {
    iapManager.purchaseProduct(productId: "premium")
}

Q: Does it work with Compose Multiplatform?​

A: Yes, kmp-iap is designed to work seamlessly with Compose Multiplatform:

@Composable
fun PurchaseButton(productId: String) {
    val scope = rememberCoroutineScope()

    Button(onClick = {
        scope.launch {
            kmpIapInstance.requestPurchase {
                ios {
                    sku = productId
                    quantity = 1
                }
                android {
                    skus = listOf(productId)
                }
            }
        }
    }) {
        Text("Purchase")
    }
}

Q: How do I share IAP logic between platforms?​

A: Create a common interface:

// In commonMain
expect class IAPManager {
    suspend fun purchaseProduct(productId: String)
    fun observePurchases(): Flow<Purchase?>
}

// Platform-specific implementations
actual class IAPManager {
    // iOS/Android specific implementation
}

Troubleshooting​

Q: My app was rejected for IAP issues. What should I check?​

A: Common rejection reasons:

  1. Missing restore functionality: Always provide restore purchases option
  2. Incorrect product types: Ensure consumable/non-consumable types match usage
  3. Price display: Show localized prices from store data
  4. Terms compliance: Follow platform guidelines for IAP UI

Q: Why are my products not loading in production but work in testing?​

A: Check:

  1. App review status: App must be approved and live
  2. Product review status: Products must be approved
  3. Regional availability: Products might not be available in all regions
  4. Time delay: Products can take 24+ hours to propagate globally

Q: How do I debug IAP issues?​

A: Enable debug logging:

// Add logging to your IAP operations
scope.launch {
    kmpIapInstance.purchaseErrorListener.collect { error ->
        println("[IAP Debug] Error: ${error.code} - ${error.message}")
    }
}

Check console output for detailed error information.

Support & Community​

Q: Where can I get help?​

A: Multiple support channels:

Q: How do I report bugs?​

A: Create detailed GitHub issues with:

  • Platform and version information
  • Steps to reproduce
  • Expected vs actual behavior
  • Relevant code snippets
  • Console logs with debug mode enabled

Q: Can I contribute to the project?​

A: Yes! Contributions are welcome:

  • Report bugs and issues
  • Submit pull requests for fixes
  • Improve documentation
  • Help answer community questions

See the Contributing Guide for details.

Still have questions? Check our Troubleshooting Guide or open a discussion on GitHub.