In GA4, how can I get another subdomain to reflect as a referrer to this one? (The opposite of referrer exclusion)

Question

We run an online ordering ecommerce SAAS platform for our customers. Typically our customer's whitelabeled ordering site would be https://app.somedomain.com. The same company will have a marketing site https://somedomain.com and possibly another like https://location.somedomain.com.

In Universal Analytics, because we didn't apply domain referral exclusions for these domains, they reflect as referrals, which is what we want.

In GA4, despite not having referral exclusions set, we are not seeing these referring sites reflecting in GA4.

I am expecting GA4 to work like UA (that is, traffic from other subdomains reflects as referral), but it doesn't. When enabling GA Debug and viewing the output in GA4 DebugView, I can see that for every page view on https://my.somedomain.com where https://other.somedomain.com is the referrer, I can see that a parameter "ignore_referrer" is true. However we have added no referral exclusions for the subdomain or main domain to the exclusion list in the data stream config.

The only possible reason for this I can think of is that GA4 automatically flags subdomains as internal referrers and excludes them?

This seems to be confirmed by this article https://support.google.com/analytics/answer/10327750?hl=en

Specifically under "Automatic self-referral detection".

So if all the above is true, how do I get this traffic to show up as referral, like it did in UA?

Answer 1

Maybe not the best solution but you could add utm tags to your 'internal' links across your subdomains. This might not even start a new session but the subdomains will be reflected in your event-based attribution reports.

Answer 2

You can make an exploration or, better, a looker studio report with Page referrer and event name for dimensions and event count for the metric. Filter your page referrer for the domain you're wanting to refer from and filter event name for either page_view or session_start (I'm still deciding on what's the most accurate).