Cannot add new user

I have a subsite I am trying to create a new user for without sending a confirmation email. Nothing happens and when I look are “all users” the user is just the superuser admin (me). If I try to add the user again I am told the email is already in use.

I need to create unconfirming users quite often for support so how do I do it?

The page I need help with: [log in to see the link]