---
title: Sending conversions back to ad platforms
description: How pixels return your conversion data to Facebook and the other platforms, so their algorithms optimize toward buyers.
updated: 2026-07-30
order: 4
related: [/guides/first-campaign, /concepts/attribution, /concepts/vocabulary]
---

A pixel is how conversions get *out* of PostbackX and back to the ad platform. It
is the opposite direction from a [postback](/reference/postback), and it is the
step that changes what the ad platform's algorithm does.

## Why it matters more than it sounds

An ad platform optimizes toward whatever outcome you report. Report nothing and it
optimizes for clicks, because clicks are all it can see — and the cheapest clicks
come from people who click a lot and buy nothing.

Send conversions back and it can optimize toward people who actually convert. Same
budget, different audience. This is usually the largest single improvement available
to a new account, which is why it is worth doing before scaling spend.

## Add one

Go to [Pixels](https://app.postbackx.com/pixels) and add a pixel for each platform
you buy traffic on. The page has a **How it works** walkthrough.

For **Facebook** you need two values, both from Events Manager:

- The **Pixel ID**
- A **Conversions API access token**

Other platforms differ in detail; the page asks for what each one needs.

Once a pixel exists, assign it to your campaigns. Conversions then flow
automatically — there is nothing further to maintain.

## Server-side, not browser-side

PostbackX sends conversions from its servers to the platform's API — for Facebook,
the Conversions API, usually written CAPI.

This matters because the browser is unreliable: ad blockers, tracking prevention
and closed tabs all lose browser-fired events. A server-to-server event does not
depend on the visitor's browser still being open, or cooperating.

## Match quality

Facebook has to decide *which person* a conversion belongs to. The more identifying
signal an event carries, the more often it succeeds, and the metric for this is Event
Match Quality in Events Manager.

Two things raise it:

**The `_fbp` and `_fbc` cookies.** These exist only in the visitor's browser, so
capturing them needs a page of yours with a
[tracking snippet](/reference/snippets) on it. This is the main reason to use a
[landing page](https://app.postbackx.com/landing-pages) on Facebook traffic rather
than sending clicks straight to the offer.

**Advertiser parameters.** `adv1` through `adv10` on a
[postback](/reference/postback) are forwarded into the CAPI event. If your offer
source can pass back hashed contact details, they go here.

## Check it arrived

Events Manager shows received events within a few minutes. Fire a test conversion —
the `curl` in [conversions are missing](/guides/missing-conversions) — and watch for
it there.

If the conversion is in PostbackX but not in Events Manager, the pixel is either not
assigned to that campaign or its access token has expired. Tokens do expire, and the
symptom is optimization quietly getting worse rather than an error, so it is worth
checking when performance drifts for no other reason.