Users are created to AutoInvoice based on an email address. Creation happens at the time of the company account opening, or separately over API or user interface. A user can be connected to many companies and a company can have many users.
Created company user can be real person or an api-user that is a technical user only. Same api-user can be added to multiple accounts, but usually for integrators with larger amount of customers it is for security reasons recommended to have own api-user per account. For example email could be formatted as AutoInvoiceuser+companyBID@example_domain.com.
Access to AutoInvoice web user interface requires access to user email for authentication. If the new users will log in to UI make sure they have access to their email address.
You can control the user rights by changing the user role. There are two roles, user and admin user. Compared to admin, users have more limited rights to service, they cannot for example modify company details or settings or add new users to the company.
You can configure user specific setting in AutoInvoice, e.g. notifications which user would like to get.
API methods for user management