How do you troubleshoot GA4 cross-domain tracking when sessions keep restarting?

Start by proving whether the linker parameter and GA4 client/session identifiers are surviving the domain transition. Do not begin by changing attribution settings.

Implementation checklist:

1. Confirm both domains send to the same GA4 property and intended web data stream. A second measurement ID on the checkout domain can create a completely separate user/session history.

2. Configure cross-domain measurement in the Google tag settings for every domain that participates in the journey. Use exact domains rather than broad patterns when possible.

3. Click from domain A to domain B and inspect the destination URL. You should see the Google linker parameter appended during the transition. If it never appears, the link is probably being rewritten, redirected, or opened in a way that prevents decoration.

4. Check redirects. Server-side redirects, URL shorteners, payment gateways, consent tools, and JavaScript routing can remove query parameters. Follow the complete redirect chain and verify the linker survives until the destination page loads.

5. Inspect GA4 requests in the browser network panel or Tag Assistant. Compare client_id and session_id values before and after the transition. If they change, the issue is continuity, not reporting attribution.

6. Review unwanted referrals only after continuity is working. Adding a payment or booking domain to unwanted referrals can suppress a referral source, but it does not repair a broken cross-domain identity handoff.

7. Test with consent states that match production. If analytics storage is denied on one domain and granted on another, behavior can differ from a fully consented test.

Document the exact click path and capture the IDs on both sides. Once the same client and session persist across domains, attribution cleanup becomes much easier.