I am getting the same thing. I have two custom domains configured on iCloud. For one I get the same msg as above "1 tester has an invalid name or email address and wasn’t added." with the other it accepts the email, invited received. The first one that fails, is my Apple ID though so I would like to use that.

I am having a related issue. The option to simulate locations seems to be missing from the scheme editor. Our QA team requires builds set to various locations for testing. Is it still possible to create builds to run on device (not in the simulator) with fake locations?