If you want to add more users and receive the following error:
Your administrator can Deactive non-users or cancel any outstanding Invites that exist. This will free up licenses for you to add users. If this has been done then the SuperAdmin or Billing user if can click on the "purchase additional users" link. Our Billing screen is where additional licenses can be purchased.
Once on the Billing screen, you will see the existing subscription. To purchase additional licenses click on "Add/Edit" found at the far right of the screen.
Add the number of new licenses you want in the Total Licenses. The licenses will be added and an invoice will be sent.