TestFlight app “invalid code” error - what to do

The TestFlight app "invalid code" error is a common issue that users may encounter while trying to use the app. Some users have proposed different solutions to address this error. One of the solutions involves adjusting the account settings from internal and external to only internal testing. It appears that TestFlight external only allows one device per external user, which can lead to issues when Apple introduced support for teams and testing of multiple versions.

To resolve the "invalid code" error, here are some steps that users can take:

1. Remove yourself from the list of internal and external testers and then re-add yourself as an internal tester.
2. Remove the user from iTunes Connect Users and Roles by clicking edit, then delete, and add them again by navigating to My Apps > TestFlight > iTunes Connect Users and adding users via the plus sign.
3. Ensure that the user receives an invitation email and can use it by logging in with the same email associated with their Apple ID.

The situation around the TestFlight error remains unresolved by Apple, and users may continue to experience challenges with the app. It is important to follow the steps outlined above to potentially address the "invalid code" error and regain access to TestFlight for testing purposes.