Thanks @mantasoff, that worked. For clarity, signing out the default user and the sandbox user, then signing in the default user to another account which has been added to testflight allowed us to make purchases again. Still unclear as to why the original user is having issues, will try to update if we get to the bottom of it.

Hi @birdmichael and @marcin1989, We are also seeing this issue in TestFlight and Debug builds, with and without Sandbox users. We are using React Native IAP as an intermediary library (v10.1.3) We have managed to get some successful purchases, notably on a Debug build from Xcode 15.2 with a new sandbox user on a tvOS 17 device. Unclear whether that is related, but I figure more info is better.