RMS invite new user error

I want to invite a new user in RMS. I did successfuly for 2 different emails, but suddenly with a third email address I get this error below the email field

The email has already been taken.

But the email is not on the list of users. I had invited a similar email (one letter was wrong) and already deleted the invitation. May that be the reason? How to fix this now?

Hello,

The user you are trying to invite most likely already has an RMS account. In that case, they might need to use a different email for an RMS account with a role in your company.
Alternatively, you can contact your sales manager and they will arrange for the old account to be deleted.

Best regards,