No TestFlight invite email gets sent for internal users

Question

I set up my application for TestFlight. For external users it is waiting for review. But if I want to invite internal users, I select them and press invite. iTunes Connects says

Answer 1

I've been round and round on this as well. What finally worked for me was to clear the internal tester status on the user, double check that the account was removed from the Internal / External list and then re-enable tester status for the user. Invite as an internal tester then worked for that user.