Hi, I have gone through your requirements, you want to integrate a payment gateway with WHMCS, and Payment processing happens with API. would you please share the backend access and documentation as well?
I have Skills in PHP, WordPress(CMS), Woo-Commerce, HTML5/CSS3, JavaScript, Bootstrap, PSD to HTML, Website design, CSS, Responsive and Interactive Website, CI and laravel, Graphic Design, Photoshop, Logo Design etc.
We are Professional 9+ years experienced developers and designers with similar expertise.