hey @DTS Engineer Albert, Hey Albert, I finally managed to try it on another device, and the solution is clearly documented (see the StackOverflow link). Basically, you need to sign out of Media & Purchases in order to use your Business Apple ID. Thanks anyway for the suggestions!
https://stackoverflow.com/questions/28488108/specify-different-email-address-for-test-flight
Topic:
App Store Distribution & Marketing
SubTopic:
TestFlight
Tags: