Cannot use proper sandbox account for internal tester on TestFlight

I cannot test IAP using sandbox account that I logged on from settings, it keeps show my regular Apple ID when I try to test IAP from TestFlight

This issue frustrate me and bunch of my colleagues, we cannot manage our subscription when sandbox account is default choosing Apple ID

I've seen people complaining about this issue a lot

Any help on resolving this issue would be really appreaciated

Cannot use proper sandbox account for internal tester on TestFlight
 
 
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