User ID

To improve cross-device attribution, it’s necessary to implement the tracking of the user ID in Google Analytics.

For GA4 via Tag Manager:

Pass the Parameter to dataLayer: On every page load after login, pass the relevant parameter user_id to your dataLayer.

Create a Variable inside GTM that reads that value from the dataLayer.

Send the property to Google Analytics via Google Tag Manager (GTM) or gtag.js:

Under the Configuration Parameter section of your GA4 Google Tag, add a new row with the user_id property and the corresponding Value (the Data Layer variable you created in step 2).

For GA4 using gtag.js

Config parameter - User ID (user_id)

Pass a unique user ID after login to track users across sessions on different devices.

Example for gtag.js:

javascript
gtag('config', 'STREAM_ID', {
  'user_id': 'USER_ID' 
});