In WHMCS, navigate to Setup > Support > Support Departments
Note down the file path in the Ticket Importing using Email Forwarders section
Login to cPanel and click Forwarders
Click Add Forwarder
1. Specify the email address of your support department. In this example it's "support"
2. Click Advanced Options
3. Select Pipe to a Program
4. Paste in the file path you noted down earlier.
5. Click Add Forwarder
N.B. With cPanel it is not necessary to copy the entire command presented in the WHMCS Support departments page, only the path to the pipe.php file.