Your Outpost subscription fee is based on the number of users you have in your account.
Adding users to your account
Account Owners and Administrators can add users at any time by issuing a user invitation. Once the recipient accepts the invitation, the monthly or annual fee for that user is automatically added to your account billing.
Removing users from your account
Account Owners and Administrators can also remove users from the account at any time. Once a user is removed, the monthly or annual subscription fee will be reduced automatically.
Note: When a user is removed, all conversations assigned to that user will be unassigned. Please see the link above for more details.