Future<void> initializeIap() async {
    iapAvailable = await _iap.isAvailable();
    if (iapAvailable) {
      await _getProducts();
      await _getPastPurchases();
      _subscription = _iap.purchaseUpdatedStream.listen((data) {
        _purchases.addAll(data);
        _verifyPurchase();
      });
      _verifyPurchase();
    }
  }

Future<void> _getPastPurchases() async {
    QueryPurchaseDetailsResponse response = await _iap.queryPastPurchases();
    //TODO: IOS Complete Purchases
    for (PurchaseDetails purchase in response.pastPurchases) {
      if (Platform.isIOS) {
        InAppPurchaseConnection.instance.completePurchase(purchase);
      }
    }
    _purchases = response.pastPurchases;
  }

Future<void> _getProducts() async {
    Set<String> ids = Set.from([offerId]);
    ProductDetailsResponse response = await _iap.queryProductDetails(ids);
    _products = response.productDetails;
    notifyListeners();
  }