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Cross-domain tracking in GA4 can be a bit tricky with separate GTM and GA4 setups. The official documentation notes that you need a shared data stream, as it helps Google Analytics understand that user interactions across the two domains are from the same user session. However, this doesn’t necessarily mean you need to blend your data.
Creating a new GA4 property for cross-domain tracking could be effective. You’d want to add a config tag with the new measurement ID to both GTM containers. The idea here is to have a separate stream of data that’s only for cross-domain tracking. You don’t need to limit this tag to only the event triggered by a click on an outbound link from domain A. It should track all user interactions across both domains.
For domain B, and also for domain A, you should certainly assign the config tag with the new data stream to all events. This will enable GA4 to follow the user as they move between the two domains and build a complete picture of their behavior. Again, this doesn’t necessarily mean that you’re blending your existing data. You’re just creating a supplementary stream that specifically tracks users who move between the two domains.
Remember, you aren’t losing any of the individual data from each website setup. This data is still tracked individually by each domain’s unique GTM and GA4 setup. The new GA4 property is in addition to, not in place of, your existing setups. It’s simply a way to give you insight into user behavior that spans both domains. Just make sure to keep all your events, conversions and other configurations consistent between the domains.
If you still have queries or run into issues, don’t hesitate to seek advice from a GA4 implementation specialist or attend one of Google’s dedicated training sessions.
