@DTS Engineer, we are experiencing the exact same issue as @biggreydog. Can this issue we escalated to allow TestFlight app to be used with Federated Apple Business Manager accounts? We are forced to use unmanaged AppleID's on our company managed devices. Our company is expected to adhere to strict security standards in our app development and it seems counterintuitive to Apple's constant messaging about security to not allow managed/federated accounts to use this development application.