A server-to-server HTTP callback that reports a conversion and its payout back to the traffic source, without a browser pixel.
A postback is a server-to-server (S2S) request used to notify the party that sent the traffic that a conversion occurred. Being server-side, it does not rely on cookies or a browser pixel, so it is unaffected by ad blockers, ITP/cookie restrictions, and cross-domain limits that break client-side tracking.
The URL typically carries a click or sub id to attribute the conversion, plus the status and payout. Conventionally the source fires a click-time postback to register the visit and the advertiser (or CRM) fires a conversion-time postback on the action.
In a lead CRM the postback closes the loop: on a conversion event (a first deposit, a registration, or a call status) the system posts the payout and attribution back to the traffic source, and can also relay the conversion to ad platforms (Facebook CAPI, Google Ads, GA4) so they optimise on it.