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?