Cross-Domain Tracking Misconfigured

Many real funnels span domains: a Shopify store with a `shop.brand.com` checkout, a SaaS marketing site with a `app.brand.com` signup flow, a hotel website with a `book.brand-reservations.com` engine, a charity with a `donate.thirdparty.org` form. The GCLID is stored in the `_gcl_aw` first-party cookie on the original domain. Without auto-link configuration, that cookie does not follow the user to the second domain. The browser's same-origin policy prevents it. The Conversion Linker tag accepts a list of domains it should auto-decorate outbound links with the linker parameter (`_gl=...`); the receiving domain reads that parameter and re-establishes the `_gcl_aw` cookie there. If the funnel crosses a domain not in the list, the GCLID is lost, the conversion is attributed to a different source or direct, and Smart Bidding learns from a degraded signal. The check fires when AdLint sees container hostnames that suggest a multi-domain funnel but the linker domain list is empty or too narrow.

1. List every domain that can appear in the conversion funnel, including payment processors, booking engines, partner platforms, and any subdomain that hosts forms or checkout.
2. In GTM, open Workspace → Tags → the Conversion Linker tag → Linker Settings.
3. Enable "Automatically link domains" and paste the comma-separated list of all funnel domains.
4. Confirm the Conversion Linker still fires on All Pages so outbound links from any page get auto-decorated.
5. In Preview mode, start on the source domain, click a link to the destination domain, and inspect the URL. it should contain a `_gl=` parameter.
6. Open Application → Cookies in DevTools on the destination domain and verify `_gcl_aw` is set. Publish only after the round-trip works on the real navigation path, not a direct page load.