The title of your ticket implies that you are trying to add
a Super User to the site. This has never been possible. You cannot add a new user when restoring, only change an existing one.
The body of your ticket implies that maybe you are
trying to change an existing Super User. In this case you must provide the numeric ID of the existing Super User in adminID per our documentation
; that's how the Super User is located on the site. You can then change the email and password of the user.
You can no longer change the username. The documentation needs to be updated. If that's what you are having trouble with, you're right; the documentation is wrong and I'll update it. The ability to change the username was removed about three years ago. We had noticed several problems regarding the uniqueness of the username, third party plugins which mandated a specific format for it and third party extensions which saved the username instead of the user ID in their database tables. In all of these cases changing the username would cause unavoidable side-effects that made it impossible to access the restored site.