Configure cross-domain tracking

We have sales flows split between checkout.example.com and www.example.com. Make cross-domain session tracking so returning visitors who move between the storefront and checkout keep the same session and client ID. Apply the solution for cookies and linker parameters to all links and forms that go between the two domains, and confirm transactions in the ecommerce report still attribute to the original campaign. Test with a Chrome and Safari purchase path and report back.

Users coming from the product pages are being counted as new sessions once they hit checkout.example.com; finance has noticed conversion drop in last week’s report. I’ve already enabled linker and added the allowed domains list. I don’t know whether the payment redirect, cookie settings on checkout, or a misconfigured linker is causing it. What is the likeliest diagnosis and the next steps to confirm and fix before the weekend campaign?

Each time we update front-end or payment flows, cross-domain tracking breaks and attribution shifts, forcing hours of firefighting. Where should I create friction to stop regressions: which tests, deployment hooks, and documentation will keep session continuity stable across domain changes? Recommend a small durable checklist the team will actually follow.