I'm trying to add a new user to an App Store Connect organization account (I have admin privileges) but the validation tells me that I cannot do it, because this user already has Apple ID - "Enter an email address that has never been associated with an Apple ID.". It happens for two different organizations but only for one email address / apple id (another one works fine). I assume it's just a bad validation message and there is something wrong with the Apple ID, but there is no way of knowing what it might be.