I'm experiencing the exact same issue. App: PureJournal (Apple ID: 6787437208) Both internal and external testing groups fail with a generic validation error when trying to assign a build to a testing group or save "What to Test" info. I've confirmed the same error occurs with a completely new, minimal test app as well, so it doesn't seem to be specific to my account or app configuration. Sounds like the same backend issue (beta contract not properly attached) affecting other developers. Thanks for sharing this.