To set up server-side tagging for mobile apps using Google Tag Manager, follow these steps:

1. Get your app ready for server-side tagging:

   • For iOS: Enable the server-side tagging upload feature and set up the custom URL scheme for server-side tagging debug mode in the Info.plist file.

   <?xml version="1.0" encoding="UTF-8"?>
   <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
   <plist version="1.0">
   <dict>
   ...
           <key>CFBundleURLTypes</key>
           <array>
                   <dict>
                           <key>CFBundleTypeRole</key>
                           <string>None</string>
                           <key>CFBundleURLName</key>
                           <string>BUNDLE_ID</string>
                           <key>CFBundleURLSchemes</key>
                           <array>
                                   <string>tagmanager.sgtm.c.BUNDLE_ID</string>
                           </array>
                   </dict>
           </array>
           <key>GOOGLE_ANALYTICS_SGTM_UPLOAD_ENABLED</key>
           <true/>
   </dict>
   </plist>
   

   • For Android: Enable the server-side tagging upload feature and set up the custom URL scheme for server-side tagging debug mode in the AndroidManifest.xml file.

2. Configure your server container to support mobile traffic:

   • Set up the Google Analytics: GA4 (App) client in your server container.
   • Configure your Google Analytics: GA4 tag to send data to Google Analytics.
   • Set up triggers for mobile traffic.

3. Enable server-side tagging in your GA4 property:

   • In your Google Analytics 4 property, go to Admin > Data streams > Select your application's stream configuration.
   • Click Configure SDK settings, then Configure server-side Tag Manager.
   • Toggle the Send data to a server-side Tag Manager container and copy the server container URL.
   • Select the percentage of traffic you want to route to the server container and click Save.

The prerequisites for setting up server-side tagging for mobile apps are:

• Google Analytics for Firebase SDK: Include the Google Analytics for Firebase SDK in your app and connect it to your Google Analytics 4 property. Learn more about the Google Analytics for Firebase SDK.
• Google Tag Manager account and server container: You need a Google Tag Manager account and a server container. If you don't have one, create a new Tag Manager account and container.
• Tagging server: Set up a tagging server to handle the server-side tagging process.

To configure the Google Analytics: GA4 (App) client in Google Tag Manager:

1. In your server container, go to Clients and click New.
2. Click Client Configuration, then select Google Analytics: GA4 (App).
3. Enter a name for your client and click Save.

This client will intercept incoming Google Analytics 4 events and generate event data objects that can be passed to a destination like Google Analytics 4.

To preview and debug your server container in Google Tag Manager:

1. Select Preview while in your Google Tag Manager server container.
2. Click the More Actions icon ⋮ on the top right and select Send requests from an app.
3. Enter your app ID and click Generate QR Code.
4. Scan the QR code with your phone's camera app and interact with your app to generate preview events.
5. Click OK to close the dialog.

This allows you to test and debug your server container before publishing the changes.