"The app isn't available, Try again." on TestFlight I'm trying to set up Internal Testing for my iOS app. I've submitted the build to the app store, and it is awaiting review happily. I have a group of Technical users in iTunes Connect with Internal Testing available, and I have invited them all to test the app.

However, when any of use click the button in the e-mail (using the Mail app on the relevant device), Testflight opens and then says "The app isn't available. Try again."

Googling for this error has been completely futile (it's a googlewhack!) - is there a simple delay before the app is available? It has been several hours. Has anybody else experienced this and can maybe tell me what step I have missed?
I solved the issue by removing all Internal Testers. Then I disabled Testflight Beta Testing on the Pre-release page.

Then I enabled Pre-release, navigated to Internal Testers and selected users to invite - and that invite worked fine.