How to understand where is the problem with the error "You can't make in-app purchases in sandbox at the moment"?

Question

Apple Developer Program

I'm testing IAP, the user sees the sandbox, but when I try to purchase, I get this error "you can't make in-app purchases in the sandbox at the moment" there is no more information. I don't understand what's wrong
PS Application for tvOS

Answer 1

Log out from the main apple id, and try again. A window should pop up asking you to enter an email address, then when you enter the address of the sandbox user, everything will work correctly.
There is also a suspicion that the same sandbox user may be linked to another account (for example, you once tested another application with the same user).