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How Postback URLs Track Your Conversions When Pixels & Cookies Fail

Jun 21, 20238 min read
Marharyta Kaplia
Marharyta Kaplia, Head of Content, AdTech Expert
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Third-party cookies are on their way out, so we're looking for an alternative to pixel tracking. One of the most viable methods is server-to-server tracking. It would provide accurate metrics even in a cookieless world.

Do you still use pixels for tracking the performance of your ad campaigns? Bad news. You might be overseeing up to 20% of conversions due to technical flaws in browsers. And this number worsens as sites introduce stricter data privacy regulations and site visitors opt out of cookies.

However, there's some good news. You can track conversions with a method that isn’t affected by any of that. It’s server-to-server tracking. There is only one downside to it: implementation complexity. But if you're committed to learning it anyway and seeing its benefits, keep reading.

What Is Server-to-Server Tracking?

S2S tracking helps to track and measure the success of online campaigns and allows you to attribute conversions to the ads that brought users to your website or app. Conversion data is exchanged between servers on the backend of apps, sites, analytics platforms, and DSPs, with the help of postback URLs.

When the user interacts with an ad, makes a purchase, or submits a form, the advertiser's server creates a special code just for it. This code is then sent to the publisher's server through an HTTP request. Once it reaches its destination, the publisher's server grabs the code and connects it to the users' actions.

Why S2S Takes the Edge Over Pixels

Pixel-based tracking relies on users' browsers and devices. S2S tracking does not. This is why server-based tracking is not affected by technical flaws or privacy settings on the user's end. No ad discrepancy issues would be caused by it.

Benefit #1. The invisible hero overcoming ad blockers

Imagine a stealthy superhero, invisible to the naked eye, maneuvering through the shadows undetected. S2S tracking is just like that — evading the radar of ad blockers and privacy settings that threaten to disrupt traditional tracking methods.

With S2S tracking, your campaigns can soar high above the barriers, ensuring accurate measurement and attribution, regardless of pesky ad-blocking forces.

Benefit #2: The accuracy avenger striking the bullseye

Picture a marksman superhero, wielding a bow and arrow with impeccable precision, hitting the bullseye every time. S2S tracking possesses a similar accuracy superpower, eliminating the guesswork and delivering spot-on data.

By transmitting data directly between servers, it bypasses the pitfalls of browser-based tracking, reducing the chances of data loss or discrepancies. With S2S tracking as your ally, you'll always hit the mark when measuring campaign performance.

Benefit # 3: The affiliate wizard empowering partnerships

Envision a sorcerer conjuring magical alliances and empowering their allies. S2S tracking plays a similar role in the realm of affiliate marketing. Just as the wizard ensures fair compensation for their partners, S2S tracking guarantees accurate conversion tracking and affiliate payouts.

Let’s look at some scenarios when a conversion wouldn’t be captured if tracked by the pixel but would be captured if tracked server-side:

  • A site visitor uses the Safari or Firefox browser. By default, the browser blocks the third-party cookies your pixel tracking relies on.
  • A site page doesn't load correctly on the user's device, and some flaws with the JS code occur. The pixel code doesn't execute correctly and doesn't capture a conversion.
  • Pixel code fires once, but that very moment your conversion tracking platform's server is busy, it doesn't pick up the data.
  • You want to track conversions on a site, but the site owner refuses to add your pixel tracker because it may slow down their site load speed.
  • A person makes a conversion action in a mobile app on their iPhone, but iOS doesn't support pixel conversion tracking for user privacy concerns.

Pixel tracking accuracy is an issue as it can underreport up to 20% of conversions for the mentioned pitfalls.

Yet, none of the described scenarios would affect S2S tracking. The conversion measurement will remain excellent even after Google Chrome finally phases out third-party cookies.

How Server-Side Tracking Works

In server-to-server tracking, all conversion data is collected, stored, and exchanged on the backend of apps and websites. Backend servers run special scripts to collect data. Then, they exchange data using postback URLs.

To understand how it works, imagine you're throwing a massive party and want to keep track of all the guests who show up. Server-to-server tracking with a postback URL is like having a sneaky spy at the entrance.

Every time someone arrives (clicks on your ad), they secretly whisper their name to the spy (your server), and the spy sends you a secret message (postback URL) with all the juicy details. It's like a top-secret network of communication that helps you keep tabs on who's joining the party (tracking conversions).

What Is a Postback URL?

To get closer to the whole backend process, you need to know what a postback URL is. A postback URL is a link generated by software that needs to receive information about conversions on sites or in apps. It can be a programmatic advertising platform, an ad server, a data management platform, an analytics tool, or other parts of the advertising ecosystem.

Every tool generates its own postback URL. The link contains macros or placeholders for data points the tool needs to receive. A server on the backend of a site gets postback URLs from the tool and checks for macros. Afterward, it swaps the macros for conversion data and returns the link back.

Postback URL tracking process

Setting up Postback URL Tracking

Let’s say you run programmatic ads with Epom DSP and use conversion tracking software to orchestrate data collected from your site or app. To optimize your ad campaigns, you want these tools to communicate server to server. So, you’ll have:

  • A sending server on the backend of your tracking tool
  • A receiving server on the backend of your Epom DSP

In general, the scheme works like this: you take the Postback URL from the Epom, paste it into your tracker (which is mandatory to have), and add macros to the postback placeholders of your tracker.

By connecting two platforms, you can implement media buying optimization. You'll see conversion data in the Epom DSP analytics dashboard. Additionally, you can use this data in Epom DSP Bidding Autopilot to optimize your campaign’s CPA automatically.

Contextual Data In Postback URLs

The list of available macros can be long and vary by platform. In Epom DSP, for example, you can select from over 50 macros to transmit the details about user devices, ad placements, bid prices, etc. to your third-party tracker.

You can use $!{source} macro to indicate SSP, $!{bid} macro to capture the bid price, $!{app} or $!{site} macros to indicate where the conversion came from, and many more.

Most macros are optional. However, there is a mandatory macro to include in the link to score conversions in Epom DSP. This is the $!{tid} macro. For conversion tracking to work properly, you have to send a unique click ID (or transaction id) from the Epom DSP to your tracking tool.

For this, you need to add the macro $!{tid} to the Target URL, for example:


After the user taps on the ad, they are redirected to the advertiser's landing page, and the unique id of this action is generated. Here is an example of an advertised link with the real value:


The parameter value is generated dynamically and differs for each unique transition.

The name of the parameter (subid) could be any – for example, sub, sub1, sub_id, sid, etc. It's set and managed by your tracking platform.

The value of the subid must be saved on your tracking platform side and passed back to Epom DSP using a postback URL. An example of the postback URL (you should take a unique postback URL from your DSP account):


where {tid} is an example of the macro that will transmit each unique transaction ID generating a conversion to the Epom DSP. In your particular case, the working macro should be taken from your tracking system.

So an example of the final postback URL that should be transmitted to the Epom DSP using our last tid value is the following:


Optionally you can pass back the conversion price so that Epom DSP can calculate your revenue in the analytics. For this, you need to replace {price} with the macro of your tracking system that will send the actual CPA to Epom DSP.

Similarly you can track two additional events – for example, installation plus registration and purchase) for more detailed optimization inside Epom DSP analytics. For this purpose you can use event=1 and event=2 macro. Here is an example:

Benefits of Server-to-Server Tracking Wrapped Up

You'll get the most accurate and complete data on conversions from your ads once you set up server-to-server tracking. This tracking method is reliable for several reasons:

  1. Conversion events. Server-to-server tracking directly captures and reports conversion events from the server. This method eliminates discrepancies caused by ad blockers, cookie deletion, or cross-device tracking challenges. It provides a more comprehensive and accurate view of the conversion metrics.
  2. Fault resilience. Conversion data is stored on servers, not in users' browsers, which ensures it won't be lost. Additionally, the sending server calls the receiving server multiple times until it picks up the conversion, preventing data loss due to server overload or downtime.
  3. No fraud. Since every conversion has a unique transaction ID, the server-to-server method is fraud-prone. One conversion won’t be counted twice.
  4. Data safety. You can encrypt any sensitive data you collect and exchange server-side. Your data remains safe and secure, giving you peace of mind.
  5. Compliance. No matter what their data privacy policies are, all OS and devices support postback URL tracking. Conversions can be tracked on nearly any website and app, but the scope of available data varies.

Only server-to-server tracking can measure conversions with an accuracy approaching 100%. It's especially useful for media buyers who deal with affiliate offers and in-app ads.

Even if you don't fall into either of these categories, now is the time to get your head around it. A cookieless future is coming. At some point, you'll have to switch from cookie-based tracking to its alternative anyway. And Epom will help you to be prepared.

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