You can only add new users on Atlas via Board or Project, and only group owners may add new members.
- Go to the page “Boards” and choose which group you would like to add new members
- Click on the green "+" beside "Members"
- Enter the e-mail address and click on "Invite"
- To complete the invitation, click on "Next" and "Confirm"
The new member only will be able to register after being approved by the system administrator.