I'm trying to add an external tester in TestFlight, but the Add button is greyed out:
Is this because the app hasn't yet been approved by Apple, or some other reasons?
I tried in both Chrome 58.0.3029.110 (64-bit) and Safari 10.1.1 (12603.2.4) on macOS 10.12.5.
This same person is beta-testing another of my apps, so I'm sure the problem is not regarding their account or mine, just the particular app I'm trying to add them as a tester to.