Subscription Flow

Source Code: subscription_flow_screen.dart

This example demonstrates how to implement subscription purchases with support for upgrades, downgrades, and subscription management.

Key Features

• Fetch subscription products
• Handle subscription purchases
• Check active subscriptions
• Manage subscription upgrades/downgrades (Android)
• Listen to subscription events

Implementation Overview

1. Set Up Listeners

StreamSubscription<Purchase>? _purchaseUpdatedSubscription;
StreamSubscription<PurchaseError>? _purchaseErrorSubscription;

void _setupListeners() {
  _purchaseUpdatedSubscription = iap.purchaseUpdatedListener.listen(
    (purchase) {
      _handlePurchase(purchase);
    },
  );

  _purchaseErrorSubscription = iap.purchaseErrorListener.listen(
    (error) {
      _handleError(error);
    },
  );
}

2. Fetch Subscription Products

final result = await iap.fetchProducts(
  ProductRequest(
    skus: ['monthly_sub', 'yearly_sub'],
    type: ProductQueryType.Subs,
  ),
);

if (result is FetchProductsResultSubscriptions) {
  final subscriptions = result.value ?? [];
  for (final product in subscriptions) {
    if (product is ProductSubscriptionIOS) {
      debugPrint('iOS Subscription: ${product.displayName}');
    } else if (product is ProductSubscriptionAndroid) {
      debugPrint('Android Subscription: ${product.title}');
    }
  }
}

3. Check Active Subscriptions

// Lightweight check - returns only subscription IDs and expiry dates
final summaries = await iap.getActiveSubscriptions(['monthly_sub']);
if (summaries.isNotEmpty) {
  debugPrint('Active subscription: ${summaries.first.productId}');
  debugPrint('Expires: ${summaries.first.expirationDateIOS}');
}

// Detailed check - returns full purchase objects
final purchases = await iap.getAvailablePurchases(
  PurchaseOptions(onlyIncludeActiveItemsIOS: true),
);

4. Purchase Subscription

await iap.requestPurchase(
  RequestPurchaseProps.subs((
    apple: RequestPurchaseIosProps(
      sku: 'monthly_sub',
      quantity: 1,
    ),
    google: RequestPurchaseAndroidProps(
      skus: ['monthly_sub'],
    ),
    useAlternativeBilling: null,
  )),
);

5. Upgrade/Downgrade Subscription (Android)

await iap.requestPurchase(
  RequestPurchaseProps.subs((
    apple: RequestPurchaseIosProps(
      sku: 'yearly_sub',
      quantity: 1,
    ),
    google: RequestPurchaseAndroidProps(
      skus: ['yearly_sub'],
      replacementModeAndroid: AndroidReplacementMode.withTimeProration,
    ),
    useAlternativeBilling: null,
  )),
);

Android Replacement Modes

enum AndroidReplacementMode {
  withTimeProration,      // 1: Credit unused time towards new subscription
  chargeProratedPrice,    // 2: Charge prorated price immediately
  withoutProration,       // 3: No credit for unused time
  deferred,               // 4: New subscription starts at next renewal
  chargeFullPrice,        // 5: Charge full price immediately
}

IAPKit Server Verification

Use IAPKit for enterprise-grade purchase verification without maintaining your own validation infrastructure.

Complete Verification Flow

Future<void> _handlePurchaseWithVerification(Purchase purchase) async {
  // 1. Verify purchase with IAPKit
  final result = await iap.verifyPurchaseWithProvider(
    VerifyPurchaseWithProviderProps(
      provider: VerifyPurchaseProvider.iapkit,
      iapkit: RequestVerifyPurchaseWithIapkitProps(
        apiKey: 'your-iapkit-api-key',
        apple: RequestVerifyPurchaseWithIapkitAppleProps(
          jws: purchase.purchaseToken,
        ),
        google: RequestVerifyPurchaseWithIapkitGoogleProps(
          purchaseToken: purchase.purchaseToken,
        ),
      ),
    ),
  );

  // 2. Handle verification result
  if (result.iapkit case final iapkit?) {
    switch (iapkit.state) {
      case IapkitPurchaseState.Entitled:
        // Purchase is valid - grant access
        await grantPremiumAccess(purchase.productId);
        await iap.finishTransaction(purchase: purchase, isConsumable: false);
      case IapkitPurchaseState.Expired:
        // Subscription expired
        await revokePremiumAccess(purchase.productId);
      case IapkitPurchaseState.Inauthentic:
        // Fraudulent purchase detected
        debugPrint('Inauthentic purchase detected');
      default:
        debugPrint('Purchase state: ${iapkit.state}');
    }
  }
}

IAPKit Purchase States

State	Description	Recommended Action
entitled	User has active subscription	Grant premium access
expired	Subscription has expired	Revoke access, show renewal prompt
canceled	User canceled, may have time remaining	Check expiration date
pending	Purchase pending (parental approval, etc.)	Show pending UI
pending-acknowledgment	Needs acknowledgment (Android)	Call finishTransaction()
inauthentic	Failed validation	Do not grant access

Checking Subscription Status on App Launch

class SubscriptionManager {
  final _iap = FlutterInappPurchase.instance;
  final String _apiKey;

  SubscriptionManager({required String apiKey}) : _apiKey = apiKey;

  Future<bool> checkSubscriptionOnLaunch(List<String> subscriptionIds) async {
    try {
      // Get all available purchases
      final purchases = await _iap.getAvailablePurchases();

      // Filter to subscriptions only
      final subscriptionPurchases = purchases.where(
        (p) => subscriptionIds.contains(p.productId),
      );

      for (final purchase in subscriptionPurchases) {
        final result = await _iap.verifyPurchaseWithProvider(
          VerifyPurchaseWithProviderProps(
            provider: VerifyPurchaseProvider.iapkit,
            iapkit: RequestVerifyPurchaseWithIapkitProps(
              apiKey: _apiKey,
              apple: RequestVerifyPurchaseWithIapkitAppleProps(
                jws: purchase.purchaseToken,
              ),
              google: RequestVerifyPurchaseWithIapkitGoogleProps(
                purchaseToken: purchase.purchaseToken,
              ),
            ),
          ),
        );

        if (result.iapkit case final iapkit? when iapkit.isValid) {
          return true; // Active subscription found
        }
      }

      return false; // No active subscription
    } catch (e) {
      debugPrint('Failed to check subscription: $e');
      return false;
    }
  }
}

// Usage
final manager = SubscriptionManager(apiKey: 'your-iapkit-api-key');
final isSubscribed = await manager.checkSubscriptionOnLaunch([
  'monthly_subscription',
  'yearly_subscription',
]);

Best Practices

1. Use lightweight checks - Use getActiveSubscriptions() for quick status checks
2. Verify server-side - Always validate subscription status with IAPKit
3. Handle upgrades properly - Choose appropriate replacement mode for Android
4. Check subscription status - Verify on app launch and app resume
5. Handle expiration - Monitor subscription expiry dates and renewal status
6. Check renewals on Android - purchaseUpdatedListener doesn't fire for renewals while app is closed