I couldn't tell you a specific site, but here's an explanation of both Google's and Facebook's functionality.

FB: https://developers.facebook.com/docs/marketing-api/conversio...

Google: https://developers.google.com/google-ads/api/docs/conversion...

This is also why companies like Tealium and Segment are currently valued at billions of dollars. They provide a single middleware integration point to funnel customer data to the dozens of marketing companies that are now leveraging server-side APIs instead of browser pixels.