People who can install and test prerelease builds.
beta resource represents the people who can install and test prerelease builds. You can create and delete beta testers, add and remove them from beta groups, and assign them to an app or a build.
When you create a beta tester, they must have an email address and must be assigned to an app, a build, or a beta group. Anonymous testers added via a TestFlight public link may not have an email address.