In-App Purchase failure in the apple's review, but works in the Testflight

• Apple rejected my submission due to the failure of purchase

• The IAP works in the Testflight with Sandbox environment without any problem.

• they gave to me is just the screenshot of when the purchase failed, just purchase , return error code 0 , "An unknown error occurred"

• same issue, anyone found a solution? and hope to get @rich help, thank you very much

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.