Google Tag Manager: Cross Domain Tracking for Conversion Events

Step 1. Open Your Google Tag

In GTM, go to Tags.

Click your Google Tag (the one that loads your GA4 Measurement ID).

If you don’t already have one, create a new Google Tag and paste in your Measurement ID (G-XXXXXXX).

Step 2. Expand Configuration Settings

Inside the tag, scroll down and open Configuration Settings.
(This replaces “Fields to Set” in the old GA4 Configuration tag.)

Click Add Row.

1. Parameter Name: linker
   
2. Value:
   { "domains": ["yourdomain.com","checkoutdomain.com"] }

This tells GA4 to auto-link those domains by appending the _gl parameter when users click between them.

Step 3. Save & Publish

Save the tag.

Publish your container.

Step 4. Add Referral Exclusions in GA4

Even with cross-domain linking, GA4 may still record “self-referrals” unless you exclude them:

Go to GA4 Admin → Data Streams → Web Stream → Configure Tag Settings → List Unwanted Referrals.

Add:

• yourdomain.com
  
• checkoutdomain.com

Step 5. Test

1. Enable Preview Mode in GTM.
   
2. Click a link from Domain A → Domain B.
   
3. The URL should include a ?_gl=... parameter.
   
4. Check GA4 Realtime to confirm that it stays one session.

That’s it — in the new GTM, you use Google Tag → Configuration Settings → linker field to achieve cross-domain tracking.