Problem with Sandbox Testers

I try adding people as Sandbox Testers to my App, but Apple keeps saying that they already exist on the team, even though they're not.

It always show "A user with this email address already exists on the team"

It keeps happening with every address I try.

I can not believe it. This thread is 3 yrs old and I'm running into the same issue ..

Problem with Sandbox Testers
 
 
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