S2S Postback Explained: How Offerwall Conversion Tracking Works

If you run an offerwall, GPT site, or any rewards platform, the server-to-server (S2S) postback is the most important piece of your tracking. This guide explains what a postback is, how it works, and how to set it up correctly.

What is an S2S postback?

A postback is a server-to-server HTTP request that the advertiser (or network) sends to your server when a user completes an offer. Instead of relying on the browser, the two servers talk directly — which makes conversion tracking accurate and hard to fake.

Why server-to-server (and not pixels)?

Browser pixels can be blocked, lost, or spoofed. S2S postbacks fire from the advertiser’s backend straight to yours, so conversions are reliable even when cookies or JavaScript fail. This is why every serious offerwall uses them.

How the flow works

1. You send a user to an offer with a unique sub ID (your user/click identifier).
2. The user completes the action.
3. The advertiser fires your postback URL, passing back the sub ID, offer ID, and payout.
4. Your server validates the request and credits the user automatically.

Common postback parameters

• subid — identifies which user/click converted.
• offer_id — which offer was completed.
• payout — how much you earned.
• txid / status — transaction id and conversion status.

Security: protect your postback

Always validate postbacks before crediting: use a secret key or signature, whitelist the sender, and reject duplicates by transaction id. Never credit on an unverified request — that is the #1 source of fraud.

Testing your postback

Fire a test conversion, confirm your server receives the call with the right sub ID, and check the user is credited exactly once. Our documentation and API reference include ready-to-use postback examples.

Want reliable tracking out of the box? Integrate AdswedMedia — S2S postbacks included.