When your instance of Verify is created, by default it has 10 “user slots” defined. This is done to give you control over the maximum costs you can incur at any time for using Verify.
You are not charged for a user slot, you are only charged for each user actually defined in the system.
A user will use 1 user slot.
You can increase the number of slots available at any time by logging into the Portal (MaestroLive.com) and changing the number of slots currently assigned to your plan.