Related resourses 
No, TestFlight is currently not supported on App Automate. Apple places a restriction on the number of devices that can be used to sign in using TestFlight. Once the user breaches this limit, app installation via TestFlight is blocked. Users will have to manually login into their Apple account and delete those devices to resolve this issue. This activity usually takes a week or more to complete.
Can I install apps via TestFlight for Automation?
Did this answer your question?
Thank you for your feedback. If you need further assistance, contact support