I am unable to install my app via TestFlight.When I tap Install in TestFlight, I receive the following error message: “Could not install xxx. The requested app is not available or doesn’t exist.” The app is visible in TestFlight, but installation always fails. I would appreciate your help in identifying the cause.
The requested app is not available or doesn't exist.
You mean that you have invited yourself, already? If that's case, the only reason I can think of is that you may be using a wrong email address. If I remember correctly, you cannot use your Apple ID email address to test-flight your apps. I can be wrong. I haven't used TestFlight for 4 or 5 years.