Hi Juan,

The number of Internal Users are the real number of your active users for your subscription. Please note that portal or archived users are not included in this count.

In the above screenshot, there are 8 active users. 
If your subscription has 10 users, then you still have 2 users remaining, if your subscription has 8 users, then you don't have any remaining users.

Go to the settings app then to manage users.. you'll see the number of users of your subscription..

Thank you!