> For the complete documentation index, see [llms.txt](https://docs.adpage.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.adpage.io/app-tracking/how-app-tracking-works.md).

# How app tracking works

The route from the Firebase SDK to the ad platforms, and why app traffic needs its own client and its own tags.

## The route

```
   App (iOS / Android)
   Firebase SDK  ──①──►  GA4 data stream setting  ──②──►  Server container
   (signup, purchase)     (hands the sGTM URL                (tagging.[client].nl)
                           back to the SDK)                   │
                                                    ┌─────────┼──────────┐
                                                    ▼         ▼          ▼
                                               GA4 App    GA4 tag    CAPI tags
                                                client   → property  → Meta / TikTok
```

## The server URL is not in the app

The Firebase SDK reads the server-side GTM URL from the GA4 data stream settings, not from the app code. The app only carries a flag that says server-side upload is allowed. As long as the setting in GA4 is off, the SDK sends straight to GA4 and the server container receives nothing, no matter what the app does.

This is the single most common cause of "no app data arrives", and it is settled in GA4 Admin, per data stream, iOS and Android separately.

## App traffic arrives on its own client

A server container routes an incoming request to the first client that claims it. Firebase requests are claimed by the **GA4 App client** (in GTM: the Google Analytics: GA4 (App) client), which is a different client than the GA4 web client. A container that only has a web client answers Firebase requests with nothing useful, and no tag fires.

Because the client differs, `Client Name` is the one condition that reliably separates app traffic from web traffic inside the container.

## Why every platform needs its own tag

An app event looks different from a web event:

* there are no cookies, so no `fbp`, `fbc`, `ttp` or `gclid`,
* there is no page URL or referrer,
* the platforms require device information instead, and each one wants it in its own shape.

So you cannot point an existing web tag at app traffic and expect it to work. In practice you add, per platform, one tag configured for app events, fired by a trigger that filters on the App client.

{% hint style="warning" %}
A Custom Event trigger that only matches an event name, for example `signup`, matches that event from **every** client, app included. Existing web tags then quietly pick up app traffic and send it as web events. Add `Client Name` to those triggers when a container starts handling app traffic.
{% endhint %}

## What stays the same

The container, the tagging domain, the consent setup and the event naming are shared between web and app. You are adding a second source to an existing container, not building a second container.


---

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