Postback (S2S) vs pixel tracking: which to use and why
Server-to-server postbacks and tracking pixels compared: how each works, why cookies and ad blockers break pixels, and when a pixel is still the right choice.
Updated on 30 Oct 2026
A conversion only counts if the advertiser tells the network about it. There are two main ways to do that: a postback from the advertiser's server, or a pixel loaded in the customer's browser. They look similar in reports, but they fail in very different ways.
How a postback works
- The visitor clicks the affiliate link; the network records the click and creates a click ID.
- The visitor reaches the advertiser with the click ID in the URL, and the advertiser stores it with the registration or order.
- When the conversion happens, the advertiser's server calls the network's postback URL with the click ID.
Everything happens between servers, so the visitor's browser is not involved.
How a pixel works
- The click is recorded the same way, and the network sets a cookie in the visitor's browser.
- On the thank-you page, the advertiser loads an image or iframe from the network.
- The browser sends the cookie with that request, and the network finds the click.
Why postbacks are more reliable
| Postback (S2S) | Pixel | |
|---|---|---|
| Needs cookies | No | Yes |
| Blocked by ad blockers or browser privacy | No | Often |
| Works if the conversion happens later, offline or in an app | Yes | No |
| Can update a conversion later (approved, rejected) | Yes | No |
| Effort for the advertiser | A server call | A tag on a page |
Browsers limit third-party cookies more every year, and many visitors use ad blockers. Pixels lose a share of conversions that postbacks keep. Postbacks also let the advertiser send events that happen days later, such as a first deposit, a renewal or a refund.
When a pixel is still the right choice
- The advertiser uses a website builder or shop platform where they can add a tag but not call a URL from the server.
- A small advertiser needs to start today and will move to postbacks later.
- You need a backup while the postback integration is being built.
Security
A postback URL should only accept conversions with a valid click ID, and ideally a secret token, so that nobody can create conversions by calling the URL. Duplicate postbacks for the same order must be ignored.
In RastroAff
Each advertiser has an integration page with their postback URL and a test button, plus pixel and iframe codes for those who can't send postbacks. Every request is recorded in the postback log with the reason for any rejection. See advertiser postback. To pass conversions on to affiliates' own trackers, see affiliate postback.