What is a postback URL? Server-to-server tracking explained

Every performance campaign depends on one small, invisible message: the postback. If it is set up correctly, advertisers, networks and publishers all see the same conversions. If it is wrong, conversions go missing, publishers are not paid, and everyone argues about numbers.

This guide explains what a postback URL is, how server-to-server (S2S) tracking works, what the parts of a postback look like, and how to test one before a campaign goes live.

What a postback URL is

A postback URL is a web address that one system calls to tell another system that a conversion happened. It is sent directly from server to server, without going through the user's browser. That is why this kind of tracking is called server-to-server or S2S tracking.

In one line: a postback is the advertiser's system saying to the network, "the user from click 8f3a2c just installed the app".

How S2S tracking works, step by step

1. A user clicks a publisher's tracking link. The network creates a unique click ID for that click.
2. The click ID is passed to the advertiser, in the landing page URL or through the attribution partner (MMP) for apps.
3. The advertiser's system stores the click ID with the user's session.
4. The user converts: installs, registers, fills a form or buys.
5. The advertiser's system, or its MMP, calls the network's postback URL with that click ID.
6. The network matches the click ID to the original click and credits the right publisher. The network can then send its own postback on to the publisher's tracker.

Because nothing depends on cookies in the browser, S2S tracking keeps working when users switch apps, use private browsing or block third-party cookies. That makes it the standard for app campaigns and the most reliable choice for web.

What a postback URL looks like

A typical postback URL looks like this:

https://tracking.example-network.com/postback?click_id={click_id}&event=registration&payout={payout}

It has three parts:

• The endpoint: the network's address that receives conversions.
• Parameters: named values such as click_id, event and payout.
• Macros: placeholders in curly brackets, such as {click_id}, that the sending system replaces with real values at the moment of the conversion.

Each platform names its macros slightly differently, so the exact format always comes from the network's documentation or the MMP's partner setup.

Postback vs pixel

Postback (S2S)Pixel (browser) Sent fromServer to serverThe user's browser Depends on cookiesNoYes Works for appsYesNo Blocked by ad blockersNoOften Setup effortNeeds a developer or MMPPaste a code snippet Pixels are quick to add, but they lose conversions. For anything you pay for, a postback is worth the extra setup.

Global vs event postbacks

A global postback fires for every conversion of a given type across all campaigns. An event postback fires for a specific event, such as a first deposit, so the network can pay on a deeper action or report quality metrics. App advertisers usually send several event postbacks, one per important in-app event, so the network can optimise sources on real engagement rather than installs alone.

How to test a postback

1. Click your own tracking link and note the click ID the network created.
2. Complete the conversion yourself, or ask the advertiser to fire a test postback with that click ID.
3. Check the network's conversion report: the test should appear within a minute or two, credited to the right offer and publisher.
4. Check that the payout and event name are correct, then remove the test conversion before launch.

Common postback mistakes

• Missing or wrong macro. The URL sends the literal text {click_id} instead of the real value, so nothing can be matched.
• Click ID not passed through. The landing page or app drops the parameter before the conversion.
• Wrong event. Installs are sent where registrations were agreed, or the other way round.
• Duplicates. The same conversion is sent twice, for example on every app open.
• Special characters not encoded, which breaks the URL.

Need help with tracking?

At Adperience Media, campaigns run on our own partner panel with server-to-server tracking, and we test every postback with the advertiser before launch. If you are new to the model, read how a CPA network works, or send us your campaign details and we will reply by email.