I am getting message \"TestFlight is Currently is Currently Unavailable. Try again later\" when trying to install from TestFlight app. My outside testers get a message \"[Ap
Currently, Testflight is experiencing issues. It's always worth checking Apple's status page
I had to go to https://developer.apple.com and accept a new version of Apple's Developer Agreement
I was ultimately able to fix this message by uninstalling and reinstalling the TestFlight app from scratch. Worth a try if the other answers don't fix your problem.
Had to disable 'Use cellular data' option in Settings for Testflight. I did not have cellular data internet and was connected via wifi. Looks like testflight tried to use cellular data with that option being on.
I had this same issue when using my personal email for beta testing my app, then using my apple ID email for internal testing.
I solved this issue by removing my personal email from all testing tracks, then deleting the TestFlight app and downloading it again. I now only use the one email (my Apple ID) for all testing.
Another possible reason for this message:
You accidentally removed the affected user from the TestFlight external testers group.
Adding him again would fix the issue.