Flutter in_app_purchase, show content after purchase - flutter

Question

I take code from offical in_app_purchases documentation, purchases work correctly.
I have function that show paid content, and i need to run it after purchase done correctly, but i don't know where i need to put it, because i steel don't inderstand purchases 100% correctly.
this is my code
final InAppPurchase _inAppPurchase = InAppPurchase.instance;
final String _productID = '1d7ea644f690ffa';
bool _available = true;
List<ProductDetails> _products = [];
List<PurchaseDetails> _purchases = [];
StreamSubscription<List<PurchaseDetails>>? _subscription;
#override
void initState() {
final Stream<List<PurchaseDetails>> purchaseUpdated = _inAppPurchase.purchaseStream;
_subscription = purchaseUpdated.listen((purchaseDetailsList) {
setState(() {
_purchases.addAll(purchaseDetailsList);
_listenToPurchaseUpdated(purchaseDetailsList);
});
}, onDone: () {
_subscription!.cancel();
}, onError: (error) {
_subscription!.cancel();
});
_initialize();
super.initState();
}
#override
void dispose() {
_subscription!.cancel();
super.dispose();
}
void _initialize() async {
_available = await _inAppPurchase.isAvailable();
List<ProductDetails> products = await _getProducts(
productIds: Set<String>.from(
[_productID],
),
);
setState(() {
_products = products;
});
}
void _listenToPurchaseUpdated(List<PurchaseDetails> purchaseDetailsList) {
purchaseDetailsList.forEach((PurchaseDetails purchaseDetails) async {
switch (purchaseDetails.status) {
case PurchaseStatus.pending:
// _showPendingUI();
break;
case PurchaseStatus.purchased:
break;
case PurchaseStatus.restored:
// bool valid = await _verifyPurchase(purchaseDetails);
// if (!valid) {
// _handleInvalidPurchase(purchaseDetails);
// }
break;
case PurchaseStatus.error:
print(purchaseDetails.error!);
// _handleError(purchaseDetails.error!);
break;
default:
break;
}
if (purchaseDetails.pendingCompletePurchase) {
await _inAppPurchase.completePurchase(purchaseDetails);
CheckListModel.addPaidData(purchaseDetails.productID);
}
});
}
Future<List<ProductDetails>> _getProducts({required Set<String> productIds}) async {
ProductDetailsResponse response = await _inAppPurchase.queryProductDetails(productIds);
return response.productDetails;
}
void _subscribe({required ProductDetails product}) {
final PurchaseParam purchaseParam = PurchaseParam(productDetails: product);
_inAppPurchase.buyNonConsumable(
purchaseParam: purchaseParam,
);
}
_subscribe function start when user click on special button in ui
function that show paid contenct name is
CheckListModel.addPaidData(purchaseDetails.productID);
when function start it create file paid.paid in getApplicationDocumentsDirectory, if it doesn't exist, and add in it productID . That what must happen
Where i need to place this function?