@eskimo, The application which is not made with Xcode, has a provision profile, but App Store Connect says "Not Available for Testing".
My Googlefu appears weak as I can't seem to figure out why this is, except that it mentions you need to be using Xcode 13 or newer.
Am guessing Xcode is adding some meta data to the Info.plist file which TestFlight requires.
Is it possible to know which keys and values are required to satisfy TestFlight?
If it's not plist keys, is there something else that's needed, that can be shared? We can do this privately if desired.