Why Do I Get The Error: "Username is already in use"?
For security reasons, users have to be unique across our entire database. Every user MUST have their own, unique username. Just like an email address, a username can only belong to one single user.
This message is telling you that someone else, has already registered that username for a different account.
Ex. If you're trying to add a username of 'jsmith', it's highly likely some other user has already taken that username.