When your funnel spans multiple domains, GA4 needs to be told they're the same business.
We identify outbound links to other domains you own, check whether linker configuration is set up to pass the client ID across, validate accept_incoming settings on the receiving domain, and filter out resource domains (CDNs, fonts, scripts) that don't need tracking.
Without cross-domain tracking, every domain hop creates a brand-new visitor in GA4 — even if it's the same human clicking 'Buy now' that takes them from marketing site to checkout site. Conversion funnels break. Attribution credits the wrong source. Returning customers look like brand-new ones.
A DTC brand hosts marketing pages on Webflow at yourbrand.com and checkout on Shopify at shop.yourbrand.com. Without cross-domain, every purchase is attributed to 'direct' traffic and the brand's Facebook ad spend looks unprofitable — so they cut the ads that were actually working.
A hotel chain's main site is hotelchain.com, but the booking engine is on reservations.hotelpartner.com. Cross-domain isn't configured — so every booking appears as 'organic from reservations.hotelpartner.com' and the actual marketing channels that drove the booking get no credit.
A medical group runs five specialty practice sites that share a single appointment booking system at book.healthgroup.com. Without cross-domain, they can't tell which specialty site sent which booking — making it impossible to evaluate marketing per practice.