checkPurchase method
Performs a best-effort client-side entitlement check.
Microsoft Store add-on StoreLicense.isActive is not used because the
native property currently always returns true. A license must be present
in AddOnLicenses and its UTC expiration time must still be in the future.
An empty storeId checks whether any add-on is currently entitled.
For authoritative auto-renewal, refund, revocation and dunning state, verify the subscription with Microsoft's server-side Recurrence API.
Implementation
Future<bool> checkPurchase({String storeId = ''}) {
_ensureWindows();
return WindowsIapPlatform.instance.checkPurchase(
storeId: storeId.trim(),
);
}