purchaseProduct method
Implementation
Future<bool> purchaseProduct(String productId) async {
final product = _products?.firstWhereOrNull(
(product) => product.id == productId,
);
if (product == null) {
throw ('The product $productId is not available');
}
await _finishPendingTransaction(productIdentifier: productId);
final purchaseParam = PurchaseParam(productDetails: product);
return _iapService.buyNonConsumable(purchaseParam: purchaseParam);
}