Server Side Receipt Validation at Google Play Store

I'm developing an application for Android in Unity in which I want to use IAP.

Before a purchase confirmation I want to contact my server and make some check.

With UnityWebRequest, I'm making the POST to my server, waiting for the response and to suspend the purchase process I'm returning the Pending value.

My problem here is that even if my process is in pending status (PurchaseProcessingResult.Pending) and the error thrown by the Post, the purchase seems to be processed as Complete since I receive an email from Google Play Store in which is written I purchased the item.

If there is an error returned from the server, is there any way to make it pending and not buy item and not receive an email from Google?

Can someone help me, please?

 

You can look at the Sample IAP Project here, it has a test toggle to change from returning Complete from ProcessPurchase vs Pending https://forum.unity.com/threads/sample-iap-project.529555/