After the 14 day trial expires, customers are required to upgrade to a paid subscription. A licence must be purchased for each active user in the platform.
Within the Subscription Details section of Organization Profile Settings you will see how many Paid Licences and how many Active Licences are currently active in the platform.
Active Licences are those that have been assigned to Active Users. A licence will become active for every active user registered.
Paid Licences are the number of licences that have been purchased. The number of Paid Licences must be greater or equal to the Active Licences to avoid restrictions being enforced on your account.