Cross-Domain Tracking

Cross-domain tracking keeps a visitor recorded as the same person and session when they move between two or more separate domains you own.

Analytics normally treats each domain as its own island. If your shop lives on yourbrand.com but checkout happens on secure-pay.com, a visitor who crosses over gets counted twice: one session that looks abandoned, and one session that appears from nowhere and pays.

Cross-domain tracking closes that seam. In GA4 you list both domains under the same web data stream, and the tag passes the visitor's ID between them in the URL, usually as a _gl parameter you can watch appear in the address bar. Now the trip reads as one person: landed on yourbrand.com, paid on secure-pay.com, one conversion.

This only works for domains you control and can tag on both ends. You cannot cross-domain track a visitor onto a payment page or booking tool you do not own, so if your checkout is a hosted third-party page, the handoff can still break unless that provider supports the linking.

Same person, two addresses, one story, but only if you stitch the seam yourself.