What is Server-to-Server PostbackS2S?
A server-side callback the brand fires to confirm a conversion, instead of relying on a browser pixel.
A postback (server-to-server, S2S) is an HTTP call the brand's server makes to the tracking platform the moment a conversion is confirmed — passing the click ID and the sale details. Because it's server-side, it survives ad blockers, cookie loss and iOS tracking prevention that break browser pixels.
The tracking platform matches the click ID back to the affiliate who drove it and credits the conversion. A signature on the call proves it really came from the brand.
PayTandem's postback is HMAC-signed and idempotent: a replayed or forged call is rejected, and the same conversion can never be counted (or paid) twice.
See it in a real deal
PayTandem is an escrow-backed affiliate marketplace with first-party tracking built in.