The username should not have spaces, capital letters, or special characters. Due to the large number of users of the Campus (more than 3 million), we recommend choosing a username that is not too common, but at the same time easy for you to remember.
For example: it is likely that the username emma has already been taken by someone else (and therefore the system does not allow her to create her account). In this case you could use emmawilliams88, since probably no one else has this username, and at the same time it will be easy for you to remember.