A customer leaves a shop for an external service and returns. Reports then identify that service as a source. Inspect the actual journey before adding domains to an exclusion list.
A referral exclusion changes how a source is treated. It neither installs tracking on the external service nor replaces cross-domain measurement between domains you control. These are separate tasks.
Document the return route with test data
Use the service’s designated test mode. Record the original entry, external hostname, return address and intended measurement. Do not create a real customer order or payment for this investigation.
Establish whether the return route actually changes attribution and identify the responsible domain. Broad matching rules can affect unintended referrals. Add only justified domains using the current GA4 interface.
Repeat the journey under the same consent conditions afterward. Inspect events and later attribution in the intended report. Compare the attributed source with the original entry recorded in your test.
Document each exception’s service, purpose and owner. Reassess it when providers or return addresses change. For transitions between your own domains, also inspect cross-domain measurement.