Item provides not happening even after using Playfab payment API

Hi team,

we use Playfab payment API but at times, we find its happened that items were not provided accordingly.

Project ID : D4D8

Code we're writing is as follows:

public PurchaseProcessingResult ProcessPurchase(PurchaseEventArgs e)

{

...Other Script...

PlayFabClientAPI.ValidateGooglePlayPurchase(new ValidateGooglePlayPurchaseRequest()

{

// Pass in currency code in ISO format 

CurrencyCode = e.purchasedProduct.metadata.isoCurrencyCode, 

// Convert and set Purchase price 

PurchasePrice = (uint)(e.purchasedProduct.metadata.localizedPrice * 100), 

// Pass in the receipt 

ReceiptJson = googleReceipt.PayloadData.json, 

// Pass in the signature 

Signature = googleReceipt.PayloadData.signature 

},

result =>

{

Debug.Log("Validation successful!"); 
…InApp PurchaseUI Complete Script... 

},

error =>

{

Debug.Log("Validation failed: " + error.GenerateErrorReport()); 
…InApp PurchaseUI Complete Script... 

});
}

When using [PlayFabClientAPI.ValidateGooglePlayPurchase], we were able to see that item purchased(paid for) has been provided in to [Inventory] of the [Title Player].
However, what we're trying to say of is that [result =>, error =>] doesn't perform.

Items paid for(purchased) are provided normally to most of users, but the issue we've mentioned keep happening only to certain users over and over.
We would like to know the reason WHY and HOW to solve this problem.

Unity 3D version : 2018.3.12 ~ 2019.2.2f1
Unity IAP in use
PlayFab SDK version : up to date, at all times