If there are no user licences available you have to get more licenses. The billing is based on the amount of licences.
How to add more user licences
1 Open the Settings tab
2. Choose Licences and add-ons
3. Choose User amount and add-ons
4. Choose Edit
5. Add the wanted amount of licenses
6. Click Save.
After this, add new user(s) and fill in the basic information.
NB! By clicking on the Buy more licences button, you will be redirected to User amount and add-ons dropdown.