Unable to log in with sandbox test users on device

Question

Trying to do some In App Purchase testing, so I created a sandbox tester on itunesconnect... but when I attempt to log in as that user on my device I get an error:

Answer 1

I had this problem as well, the simple solution was to sign out of my iTunes account on my physical device, restart it, clean the project and then build and run as normally. Only sign into your test iTunes account after the restart once the project is running. This issue may be caused by the way in which Apple handles or cashes users iTunes accounts on a device.