restorePurchases method
Restore the user's previously-purchased entitlements from the store (StoreKit's transaction history / Google Play's owned-purchases query), re-submitting any found receipts so the server can (re-)grant entitlements for this subscriber. Use for the "Restore Purchases" button required by App Store review — entitlements are already synced automatically via configure/purchase receipt posting, so this isn't needed on every launch.
Implementation
Future<PurchaseResult> restorePurchases() => _platform.restorePurchases();