ConfirmPendingPurchase issue

Hello everyone!
I have a problem with the Google Play Store in unity.
I have a game with IAP. My shopping flow:

1. The player clicks the consumable button and calls IStoreController.InitiatePurchase.
   
2. After payment invokes the callback IStoreListener.ProcessPurchase where I return PurchaseProcessingResult.Pending and invoke my processing algorithm, connect to my game server, check the purchase on it and return the check result.
   
3. After a successful check on the game server, I call IStoreController.ConfirmPendingPurchase to confirm the purchased consumables.

Everything works fine, but ... If the network is disconnected in step 2 and streaming to the game server stops, then IStoreController.ConfirmPendingPurchase was not called.
After that, I reconnect to the network and reopen the app. In IStoreListener.OnInitialized (IStoreController controller, IExtensionProvider extensions) I get controller.products.all and check if any product in the list hasReceipt. If this is true, I am trying to call IStoreController.ConfirmPendingPurchase again for this product.

But I have an exception
E / Unity: Google Play Store: Failed to complete transaction with ServiceUnavailable error code and debug message: An internal error has occurred. Please consider calling FinishAdditionalTransaction using an extension.

Consumables remain pending.

P.S. If I call IStoreController.ConfirmPendingPurchase a second time within 2 seconds, the pending purchase will be confirmed successfully. But I think this is the wrong flow for this case.

 

Thanks for the quick response!

Of course not. But product with receipt is properly in Pending state and already charged. Last step is confirm this pending purchase. But i cant do it the first time. As I say "If I call IStoreController.ConfirmPendingPurchase a second time within 2 seconds, the pending purchase will be confirmed successfully."

If I don't confirm this pending purchase, a Google Play Cancellation Receipt will come to my mail shortly

Additional I can say, that while I debugging my app in Android Studio Logcat I caught this
W/BillingClient: Error consuming purchase with token. Response code: 2

Response code 2 is "Network connection is down."