Connect WHMCS for billing context and single sign-on.
In WHMCS create API credentials (identifier + secret) for a role that can read clients and tickets.
Open Admin → Channels → WHMCS (or the WHMCS SSO page) and enter the WHMCS URL, identifier and secret.
Run the connection test / dry-run preview to confirm access.
Billing context and WHMCS single sign-on are now available.