When creating a user on the VIA portal and no available licenses show, this will mean that the maximum amount of licenses have been reached and will need to increase the limit.
1) When logged into the portal, click on Billing
2) Select the License in question that needs to be increased
3) Click on the Edit button and increase the Total field by how many you need to be added and then click on Save.
NOTE: When adding extra licenses, this will occur a charge for the type of license you are adding on the portal. Make sure that if old accounts are not being used that they are deleted to make the license available for the new user being added onto the portal.