The number of licenses purchased (in your Order Form) represents your minimum.
This means that you are not restricted from adding more than your MPQ. If you do add more than the minimum users, you'll be charged the following month a pro-rated amount based on the time remaining in the subscription.
However, if you archive these users, you'll receive a credit note that will be applied to your next invoice:
In short, both the addition and removal of users is billed monthly on a pro-rated basis.
Have a question? Contact our friendly Support team via the in-app chat at the bottom-right of your screen, or email email@example.com.