In-App Purchase - App Completeness

Hello everyone, our game has already been rejected twice as they claim they fail to test in-app purchases.

This is the message by the team review:

Guideline 2.1 - Performance - App Completeness
We found that your in-app purchase products exhibited one or more bugs when reviewed on iPhone and iPad running iOS 14.6 on Wi-Fi.
Specifically, your app's In-App Purchase is unresponsive when user attempts to purchase it.
Next Steps
When validating receipts on your server, your server needs to be able to handle a production-signed app getting its receipts from Apple’s test environment. The recommended approach is for your production server to always validate receipts against the production App Store first. If validation fails with the error code "Sandbox receipt used in production," you should validate against the test environment instead.

The logic implemented for purchases is the same for other games already published and works regularly in production. Also in our internal tests (including sandbox) purchases work in-game.

Can anyone advise us what to do or have had a similar problem? We have been trying to solve for days but without success so far. Thanks for your help

Same issue as well. In the Testflight with Sandbox account, there was no issue with the purchase. The only they gave to me is just the screenshot of when the purchase failed. error code 0 , "An unknown error occurred" Is there anything that I missed? please help me

After repeated submissions and minor changes they accepted the new version. I simply added a warning showing a progress bar as the store loads but I really don't think this was the solution. I simply believe there was a problem with their test devices.

In-App Purchase - App Completeness
 
 
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