A managed user is a user that a Group Manager pays a license for.
To add a managed user: click on Manage.
First check if you still have unassigned licenses available.
If so, you can assigned one of those to the new user via the manage button.
If you don’t have any unassigned seats left, you will need to purchase a new license for the managed user.
Go to billing -> License Overview -> Add managed users.
Select monthly or yearly billing for the account and confirm.
An email will be sent out to the user to accept the license.
Once the license has been confirmed, the user had a valid paying license.