Tracking conversions on a 3rd party site

My business works with affiliates to whom we send traffic, and when a signup happens on their site, we are paid. We need a way to confirm that what they're reporting to us is accurate and trustable - so we gave them a pixel hosted on our site that would be implemented on their conversion page. Unfortunately, the data seems extremely off, and they're saying it's our pixel - not their reporting system. They recommended we get them a "Google Pixel, javascript if possible".

I've been trying to figure out how / where to do this or set this up. Any clues, guys?