Cross-domain tracking is configured if multiple domains are in use

When marketing traffic lands on www.example.com and converts on app.example.com, missing cross-domain configuration resets the session at the subdomain boundary. The user who clicked your Google Ad and signed up is recorded as two separate visitors: one that bounced on the marketing site, one that appeared from (direct) / (none) on the app. Campaign ROI gets understated, paid channels look unprofitable, and budgets move away from the channels that actually work.

Configure the GA4 linker in your gtag config so both domains share a measurement cookie:

gtag('config', 'G-XXXXXXX', {
  linker: { domains: ['example.com', 'app.example.com'] }
})

In the GA4 UI, add both domains under Admin > Data Streams > Configure tag settings > Configure your domains. For Stripe checkout redirects, fire the conversion event on your post-redirect thank-you page, not inside Stripe's domain.

• ID: marketing-analytics.core-analytics.cross-domain-tracking

• Severity: low

• What to look for: Check if the project spans multiple domains or subdomains that need to share analytics sessions. Signals: multiple domain references in config files, references to a separate app. subdomain alongside a marketing www. domain, Stripe checkout redirects (a separate domain), or explicit cross-domain linking in navigation components. For GA4: look for linker configuration. For other SDKs: look for cross-domain session handling config.

• Pass criteria: Count every unique domain and subdomain referenced in config files, navigation, and external redirect targets. Either no cross-domain tracking is needed (1 domain only), OR cross-domain tracking is configured for all 2 or more domains in the relevant SDKs.

• Fail criteria: At least 2 domains are detected (e.g., marketing site on example.com and app on app.example.com) with no cross-domain linking configured, meaning sessions will reset when users navigate between domains.

• Skip (N/A) when: The project is a single-domain, single-subdomain project with no external checkout or cross-domain flows.

• Detail on fail: "App subdomain (app.example.com) referenced in config but no GA4 cross-domain linker configured — users who navigate from the marketing site to the app will appear as new sessions"

• Remediation: For GA4, configure cross-domain measurement in your GA4 property settings (Admin > Data Streams > Configure tag settings > Configure your domains). In code, add the linker configuration:

  gtag('config', 'G-XXXXXXX', {
    linker: { domains: ['example.com', 'app.example.com'] }
  })
  

  For Stripe checkout: GA4 does not automatically follow users into Stripe's domain — configure your conversion events to fire on the thank-you page after redirect, not inside Stripe's checkout.