Affiliate Tracking pixel implementation using cURL / API

I had the affiliate tracking installed, payment and invoicing working correctly but because my site accepts payments more than once on each project, (i.e 50% payment and then a final payment a few weeks later when a project is finished) I have been told by the affiliate company i need a more advanced kind of tracking. So basically an API solution that can bridge the gap between an inquiry and invoicing. This will need developer with expertise in cURL, my site's database architecture, and scripting languages. They will need to work with a developer from the affiliate tracking company until we get things up and running correctly.