Namecheap.com SSL module for WHMCS is an open-source plugin that is distributed free of charge. This module allows you to automate SSL Certificate sales with the Namecheap platform

Pre-requisites

• Access to WHMCS admin area.
• An understanding of Namecheap’s environments.
• Namecheap account with API access enabled on the desired environment.

Important Note: 

You may find ComodoSSL in list of SSLs while setting up products in WHMCS. ComodoSSL is a test product, it is included in list of products, but it is not fully supported yet. Please do not set up ComodoSSL Products.