API Roles
From WHMCS Documentation
This feature is available in version 7.4 and above
API authentication credentials can be limited to individual API actions. This enables greater control and security when connected apps and services utilize credentials to access your WHMCS.
The API Roles you define itemize which a subset of API actions may be used. API credentials are associated with one or more of these roles. When an API request is made, if any role provides permission to the requested action, the request will be authorized and allowed to complete.