fix: some fixes in example app

lib/pages/order_confirmation.dart

@@ -118,6 +118,7 @@ class _OrderConfirmationPageState extends State<OrderConfirmationPage> {
       sum: totalPrice.toString(),
       date: '',
       providers: providers,
+      timestamp: DateTime.now().millisecondsSinceEpoch.toString(),
     );
     await addToHistory(order);
   }