Purchases

Complete guide to implementing in-app purchases with kmp-iap, covering everything from basic setup to advanced purchase handling using Kotlin Multiplatform.

Purchase Flow Overview

The in-app purchase flow follows this standardized pattern:

1. Initialize Connection - Establish connection with the store
2. Setup State Observers - Monitor purchase states via StateFlow
3. Load Products - Fetch product information from the store
4. Request Purchase - Initiate purchase flow
5. Handle Updates - Process purchase results via StateFlow
6. Deliver Content - Provide purchased content to user
7. Finish Transaction - Complete the transaction with the store

Key Concepts

Purchase Types

• Consumable: Can be purchased multiple times (coins, gems, lives)
• Non-Consumable: Purchased once, owned forever (premium features, ad removal)
• Subscriptions: Recurring purchases with auto-renewal

Platform Differences

• iOS: Uses StoreKit 2 (iOS 15.0+)
• Android: Uses Google Play Billing Client v8
• Both platforms use the same API surface in kmp-iap

Basic Purchase Flow

1. Setup Purchase Observers

Before making any purchases, set up StateFlow observers to handle purchase updates and errors:

import kotlinx.coroutines.*
import kotlinx.coroutines.flow.*
import io.github.hyochan.kmpiap.KmpIAP
import io.github.hyochan.kmpiap.data.*

class PurchaseHandler(
    private val scope: CoroutineScope
) {
    
    fun setupPurchaseObservers() {
        // Observe successful purchases
        scope.launch {
            kmpIapInstance.purchaseUpdatedListener.collectLatest { purchase ->
                println("Purchase update received: ${purchase.productId}")
                handlePurchaseUpdate(purchase)
            }
        }

        // Observe purchase errors
        scope.launch {
            kmpIapInstance.purchaseErrorListener.collectLatest { error ->
                println("Purchase failed: ${error.message}")
                handlePurchaseError(error)
            }
        }
    }
    
    fun dispose() {
        kmpIapInstance.endConnection()
    }
}

2. Using with ViewModel (Recommended)

For a more structured approach, use this purchase handler pattern:

import androidx.lifecycle.ViewModel
import androidx.lifecycle.viewModelScope

class ProductsViewModel : ViewModel() {
    private val productIds = listOf(
        "dev.hyo.martie.10bulbs",
        "dev.hyo.martie.30bulbs"
    )
    
    
    data class PurchaseState(
        val isProcessing: Boolean = false,
        val purchaseResult: String? = null,
        val products: List<Product> = emptyList()
    )


    private val _state = MutableStateFlow(PurchaseState())
    val state: StateFlow<PurchaseState> = _state.asStateFlow()

    init {
        setupPurchaseObservers()

        // Initialize connection and load products
        viewModelScope.launch {
            kmpIapInstance.initConnection()
            loadProducts()
        }
    }
    
    override fun onCleared() {
        super.onCleared()
        kmpIAP.dispose()
    }
    
    // Purchase observer setup...
}

3. Request a Purchase

Use the unified API for initiating purchases:

suspend fun handlePurchase(productId: String) {
    try {
        _state.update { 
            it.copy(
                isProcessing = true,
                purchaseResult = "Processing purchase..."
            )
        }

        // Request purchase
        kmpIapInstance.requestPurchase {
            ios {
                sku = productId
                quantity = 1
            }
            android {
                skus = listOf(productId)
                obfuscatedAccountIdAndroid = getUserId()
            }
        }
        
        // Result will be emitted via currentPurchase StateFlow
    } catch (error: PurchaseError) {
        _state.update {
            it.copy(
                isProcessing = false,
                purchaseResult = "❌ Purchase failed: ${error.message}"
            )
        }
    }
}

Product Loading

Loading Products

suspend fun loadProducts() {
    try {
        // Load products
        val products = kmpIapInstance.fetchProducts {
            skus = productIds
            type = ProductQueryType.InApp
        }

        println("Loaded ${products.size} products")
        products.forEach { product ->
            println("Product: ${product.productId}")
            println("Price: ${product.price}")
            println("Title: ${product.title}")
        }

        _state.update { it.copy(products = products) }
    } catch (e: PurchaseError) {
        println("Error loading products: $e")
    }
}

Loading Subscriptions

suspend fun loadSubscriptions() {
    try {
        val subscriptionIds = listOf("premium_monthly", "premium_yearly")
        val subscriptions = kmpIapInstance.fetchProducts {
            skus = subscriptionIds
            type = ProductQueryType.Subscription
        }

        subscriptions.forEach { sub ->
            println("Subscription: ${sub.title}")
            println("Price: ${sub.price}")
            println("Period: ${sub.subscriptionPeriod}")
        }
    } catch (e: PurchaseError) {
        println("Error loading subscriptions: $e")
    }
}

Subscription Purchases

Subscription Purchase

suspend fun requestSubscription(productId: String) {
    try {
        kmpIapInstance.requestPurchase {
            ios {
                sku = productId
                quantity = 1
            }
            android {
                skus = listOf(productId)
                obfuscatedAccountIdAndroid = getUserId()
            }
        }
        // Result via purchaseUpdatedListener Flow
    } catch (e: PurchaseError) {
        handleError(e)
    }
}

// With subscription offers (Android)
suspend fun requestSubscriptionWithOffer(
    productId: String,
    offerToken: String
) {
    kmpIapInstance.requestPurchase {
        ios {
            sku = productId
            quantity = 1
        }
        android {
            skus = listOf(productId)
            subscriptionOffers = listOf(
                SubscriptionOfferAndroid(
                    sku = productId,
                    offerToken = offerToken
                )
            )
        }
    }
}

Important Notes

Purchase Flow Best Practices

1. Always set up observers first before making any purchase requests
2. Handle both success and error cases appropriately
3. Show loading states during purchase processing
4. Validate purchases server-side for security
5. Finish transactions after delivering content

Handling Purchase Success

private suspend fun handlePurchaseUpdate(purchase: Purchase) {
    println("Purchase successful: ${purchase.productId}")
    
    // Deliver the product to the user
    deliverProduct(purchase.productId)
    
    // Finish the transaction
    try {
        val success = kmpIapInstance.finishTransaction(
            purchase = purchase.toPurchaseInput(),
            isConsumable = true // Set appropriately for your product type
        )

        if (success) {
            println("Transaction completed successfully")
        }
    } catch (e: Exception) {
        println("Error finishing transaction: $e")
    }
}

Getting Product Information

Retrieving Product Prices

class ProductInfo {
    suspend fun loadProductInformation(productIds: List<String>): List<Product> {
        return try {
            // Request products from store
            val products = kmpIapInstance.fetchProducts {
                skus = productIds
                type = ProductQueryType.InApp
            }

            products.forEach { product ->
                println("Product: ${product.productId}")
                println("Title: ${product.title}")
                println("Description: ${product.description}")
                println("Price: ${product.price}")
                println("Currency: ${product.currencyCode}")
                println("Price Micros: ${product.priceAmountMicros}")
            }

            products
        } catch (e: PurchaseError) {
            println("Error loading product information: $e")
            emptyList()
        }
    }
}

Platform Support

import io.github.hyochan.kmpiap.openiap.IapPlatform

class PlatformSupport {
    suspend fun checkPurchaseSupport(): Boolean {
        return try {
            when (kmpIapInstance.getCurrentPlatform()) {
                IapPlatform.Ios -> {
                    // Check if device can make payments
                    kmpIapInstance.initConnection()
                    true
                }
                IapPlatform.Android -> {
                    // Check Play Store connection
                    kmpIapInstance.initConnection()
                    true
                }
            }
        } catch (e: PurchaseError) {
            println("Error checking purchase support: $e")
            false
        }
    }
}

Checking Platform Compatibility

fun checkPlatformFeatures() {
    when (kmpIapInstance.getCurrentPlatform()) {
        IapPlatform.Ios -> {
            // iOS-specific features
            println("iOS platform detected")
            // Can use iOS-specific methods like:
            // - kmpIapInstance.presentCodeRedemptionSheetIOS()
            // - kmpIapInstance.showManageSubscriptionsIOS()
            // - kmpIapInstance.getStorefrontIOS()
        }
        IapPlatform.Android -> {
            // Android-specific features
            println("Android platform detected")
            // Can use Android-specific methods like:
            // - kmpIapInstance.consumePurchase()
            // - kmpIapInstance.deepLinkToSubscriptionsAndroid()
            // - kmpIapInstance.requestPurchaseHistoryAndroid()
        }
    }
}

Product Types

Consumable Products

Products that can be purchased multiple times:

suspend fun handleConsumableProduct(purchase: Purchase) {
    // Deliver the consumable content (coins, lives, etc.)
    deliverConsumableProduct(purchase.productId)

    // Finish transaction as consumable
    val success = kmpIapInstance.finishTransaction(
        purchase = purchase.toPurchaseInput(),
        isConsumable = true
    )

    if (success) {
        println("Consumable product delivered and consumed")
    }
}

Non-Consumable Products

Products purchased once and owned permanently:

suspend fun handleNonConsumableProduct(purchase: Purchase) {
    // Deliver the permanent content (premium features, ad removal)
    deliverPermanentProduct(purchase.productId)

    // Finish transaction as non-consumable
    val success = kmpIapInstance.finishTransaction(
        purchase = purchase.toPurchaseInput(),
        isConsumable = false
    )

    if (success) {
        println("Non-consumable product delivered")
    }
}

Subscriptions

Recurring purchases with auto-renewal:

suspend fun handleSubscriptionProduct(purchase: Purchase) {
    // Activate subscription for user
    activateSubscription(purchase.productId)

    // Finish transaction as non-consumable
    val success = kmpIapInstance.finishTransaction(
        purchase = purchase.toPurchaseInput(),
        isConsumable = false
    )

    if (success) {
        println("Subscription activated")
    }
}

Advanced Purchase Handling

Purchase Restoration

Restore previously purchased items:

suspend fun restorePurchases() {
    try {
        // Get available purchases
        val purchases = kmpIapInstance.getAvailablePurchases()
        println("Found ${purchases.size} available purchases")

        // Process each restored purchase
        purchases.forEach { purchase ->
            deliverProduct(purchase.productId)
        }
    } catch (e: PurchaseError) {
        println("Error restoring purchases: $e")
    }
}

Handling Already Owned Error

Handle cases where user already owns the item:

private fun handlePurchaseError(error: PurchaseError) {
    println("Purchase failed: ${error.message}")

    when (error.code) {
        ErrorCode.AlreadyOwned -> {
            println("User already owns this item")
            scope.launch {
                // Refresh available purchases
                kmpIapInstance.getAvailablePurchases()
            }
        }
        ErrorCode.UserCancelled -> {
            // User cancelled, no action needed
            println("Purchase cancelled by user")
        }
        else -> {
            // Handle other errors
            showErrorDialog(error.message)
        }
    }
}

Subscription Management

Open native subscription management:

suspend fun openSubscriptionManagement() {
    try {
        when (kmpIapInstance.getCurrentPlatform()) {
            IapPlatform.Ios -> {
                kmpIapInstance.showManageSubscriptionsIOS()
            }
            IapPlatform.Android -> {
                kmpIapInstance.deepLinkToSubscriptionsAndroid("premium_monthly")
            }
        }
    } catch (e: PurchaseError) {
        println("Failed to open subscription management: $e")
    }
}

Receipt Validation

Validate purchases server-side for security:

suspend fun validatePurchaseReceipt(purchase: Purchase): Boolean {
    return try {
        // Send to your server for validation
        val response = api.validatePurchase(
            productId = purchase.productId,
            purchaseToken = purchase.purchaseToken,
            receipt = purchase.transactionReceipt,
            platform = kmpIapInstance.getCurrentPlatform().name
        )

        response.isValid
    } catch (e: Exception) {
        println("Receipt validation failed: $e")
        false
    }
}

Error Handling

Common Purchase Errors

fun handlePurchaseError(error: PurchaseError) {
    when (error.code) {
        ErrorCode.UserCancelled -> {
            println("User cancelled the purchase")
        }
        ErrorCode.NetworkError -> {
            println("Network error occurred")
            showRetryDialog()
        }
        ErrorCode.ServiceUnavailable -> {
            println("Billing service unavailable")
        }
        ErrorCode.ProductNotAvailable -> {
            println("Requested item is unavailable")
        }
        ErrorCode.DeveloperError -> {
            println("Invalid arguments provided to the API")
        }
        ErrorCode.AlreadyOwned -> {
            println("User already owns this item")
            handleAlreadyOwned()
        }
        ErrorCode.Unknown -> {
            println("Unknown error: ${error.message}")
        }
    }
}

Testing Purchases

iOS Testing

Set up iOS testing environment:

// For iOS testing in sandbox environment
fun setupIOSTesting() {
    println("Testing on iOS Sandbox")
    
    // Use test Apple ID for sandbox testing
    // Products must be configured in App Store Connect
    // Test with different sandbox user accounts
}

Android Testing

Set up Android testing environment:

// For Android testing with test purchases
fun setupAndroidTesting() {
    println("Testing on Android")
    
    // Use test product IDs like:
    // - android.test.purchased
    // - android.test.canceled  
    // - android.test.refunded
    // - android.test.item_unavailable
    
    val testProductIds = listOf(
        "android.test.purchased", // Always succeeds
        "android.test.canceled"   // Always cancelled
    )
}

Complete Example

Here's a complete working example:

import kotlinx.coroutines.*
import kotlinx.coroutines.flow.*
import androidx.lifecycle.ViewModel
import androidx.lifecycle.viewModelScope
import io.github.hyochan.kmpiap.useIap.*
import io.github.hyochan.kmpiap.data.*

class PurchaseService : ViewModel() {
    init {
        // Initialize IAP connection
        viewModelScope.launch {
            kmpIapInstance.initConnection()
        }
    
    init {
        setupPurchaseObservers()
    }
    
    private fun setupPurchaseObservers() {
        // Observe purchase success
        viewModelScope.launch {
            kmpIapInstance.purchaseUpdatedListener.collectLatest { purchase ->
                handlePurchaseSuccess(purchase)
            }
        }

        // Observe errors
        viewModelScope.launch {
            kmpIapInstance.purchaseErrorListener.collectLatest { error ->
                handlePurchaseError(error)
            }
        }
    }
    
    private suspend fun handlePurchaseSuccess(purchase: Purchase) {
        // 1. Deliver product
        deliverProduct(purchase.productId)

        // 2. Finish transaction
        val success = kmpIapInstance.finishTransaction(
            purchase = purchase.toPurchaseInput(),
            isConsumable = true
        )

        if (success) {
            println("Transaction completed")
        }
    }
    
    private fun handlePurchaseError(error: PurchaseError) {
        if (error.code == ErrorCode.AlreadyOwned) {
            // Handle "already owned" error
            viewModelScope.launch {
                kmpIapInstance.getAvailablePurchases()
            }
        }
    }
    
    suspend fun purchaseProduct(productId: String) {
        kmpIapInstance.requestPurchase {
            ios {
                sku = productId
                quantity = 1
            }
            android {
                skus = listOf(productId)
                obfuscatedAccountIdAndroid = getUserId()
            }
        }
    }
    
    override fun onCleared() {
        super.onCleared()
        kmpIapInstance.endConnection()
    }

    private fun deliverProduct(productId: String) {
        // Implement your product delivery logic
    }
    
    private fun getUserId(): String {
        // Return user ID for fraud prevention
        return "user_123"
    }
}

Compose UI Integration

@Composable
fun PurchaseScreen(viewModel: PurchaseService = viewModel()) {
    var products by remember { mutableStateOf<List<Product>>(emptyList()) }
    var isConnected by remember { mutableStateOf(false) }
    
    Column {
        // Connection indicator
        if (!isConnected) {
            Card(
                backgroundColor = Color.Red,
                modifier = Modifier.fillMaxWidth()
            ) {
                Text("Store not connected", color = Color.White)
            }
        }
        
        // Products list
        LazyColumn {
            items(products) { product ->
                ProductCard(
                    product = product,
                    onPurchase = {
                        scope.launch {
                            viewModel.purchaseProduct(product.productId)
                        }
                    }
                )
            }
        }
    }
}

This guide covers the complete purchase flow using the kmp-iap API, with examples demonstrating the Kotlin Multiplatform approach to in-app purchases.