> ## Documentation Index
> Fetch the complete documentation index at: https://docs.datalyr.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Cross-domain tracking

> Preserve supported attribution across websites and checkout domains.

Cross-domain tracking matters when a journey leaves one domain before conversion—for example, a marketing site sending a customer to a separate app or checkout.

## Map the journey first

Write down every owned domain, third-party checkout, redirect, and mobile handoff. Mark where campaign context is captured, where the user becomes known, and where revenue is created.

## Supported setup

1. Install Datalyr for the same workspace on each domain you control.
2. Use consistent campaign parameters on the first landing page.
3. Identify the customer with the same stable application ID wherever it is known.
4. For CheckoutChamp, add the checkout hosts under **Settings → Identity & Attribution**.
5. For Shopify guest checkout, use **Shopify cart attribution** when appropriate.
6. Use tracking links or documented platform bridges for web-to-app handoffs.

Do not invent a URL parameter containing a raw visitor or user ID. Arbitrary identity decoration can leak identifiers through browser history, analytics, logs, and referrer headers.

## Test end to end

Start in a private window with recognizable UTMs, cross each domain once, and complete a test conversion. Confirm the initial event, the known user journey, the revenue event, and the conversion record.

<Note>
  Third-party domains you cannot instrument may break browser continuity. A stable known-user identity or supported checkout integration can still connect the server-side conversion, but only when the required context was preserved earlier.
</Note>