We charge based on the number of active collaborators in your repository. Active collaborators are defined as the collaborators who have created a Pull Request and have used Aviator on their PRs. You can review the count of Billed users in the Billing section of Aviator.
A collaborator is a GitHub user associated with the organization or repository. A user, on the other hand, is someone who has access to the Aviator dashboard. There is no cost associated with the number of users you have in your Aviator account for any plan, you only pay based on the number of active collaborators.