Two owned domains belong to one user journey, but measurement does not connect them as intended. Inspect the real transition as well as GA4 settings. Redirects can remove parameters needed for the configured linkage.
Google’s cross-domain measurement may append a _gl parameter. Treat it as a generated technical value rather than a field for customer information. Do not copy these values into public bug reports.
Follow a controlled transition
Use genuinely associated domains or an appropriate test environment. Check shared measurement configuration and GA4 domain rules against the tags and data stream actually in use.
After the intended consent, follow the transition and every redirect. Does the required parameter survive to the appropriate destination? Do both sides load their intended tags? Compare the actual network requests from both pages.
Where both links and forms are used, inspect them separately. A successful link transition does not automatically validate a form submission route.
Record whether the parameter existed and survived, rather than storing its raw value. Use diagnostic tools and non-personal test journeys to assess measurement. Excluding referrals from an external payment domain is a different configuration and does not automatically connect two domains you control.