GA4 Cross-Domain Tracking Not Unified Across Subdomains

What Happened

All four A Square Solutions properties share one GA4 property (G-MPQVF41ZYM) and had the tracking tag installed correctly on each:

• asquaresolution.com (WordPress)
• lab.asquaresolution.com (AI Execution Lab)
• trustseal.asquaresolution.com (TrustSeal app)
• scamcheck.asquaresolution.com (ScamCheck app)

The GA4 tag was working — pageviews were being recorded on every property. The problem was identified while reviewing the Acquisition report: direct traffic numbers were unusually high relative to expected referral patterns. The session count per page was also higher than the pageview-to-session ratio should be.

The signal that revealed the issue: a test navigation from asquaresolution.com to scamcheck.asquaresolution.com, checked in GA4 Realtime, showed two separate active users — not one.

Why GA4 Breaks Sessions Across Subdomains

GA4 sets a first-party cookie (_ga) on the user's browser to maintain session and user identity. By default, this cookie is scoped to the exact hostname — asquaresolution.com sets a cookie for asquaresolution.com, and scamcheck.asquaresolution.com sets a different cookie for scamcheck.asquaresolution.com.

When a user navigates from one subdomain to another:

1. The browser leaves the first domain — GA4 session ends
2. The browser arrives at the second domain — GA4 finds no cookie, starts a new session
3. The new session is attributed to "direct" because there is no referrer (or the referrer is filtered out as same-domain)

The result: one user journey appears as two or more sessions, each starting from "direct."

The Fix

Step 1: Configure cross-domain measurement in GA4

GA4 Admin → Data Streams → Web stream → Configure Tag Settings → Configure your domains.

Add: asquaresolution.com

GA4 automatically includes all subdomains when the parent domain is configured. This tells GA4 to pass session information via URL parameters when navigating between these domains.

Step 2: Update gtag configuration on all properties

For each property's GA4 tag installation, add cookie_domain:

gtag('config', 'G-MPQVF41ZYM', {
  cookie_domain: 'asquaresolution.com'
});

Setting cookie_domain to the parent domain means the _ga cookie is set at asquaresolution.com level — accessible to all subdomains. A user's identity persists as they navigate across the ecosystem.

For the WordPress main site (asquaresolution.com), the gtag config is managed through the GA4 WordPress plugin settings or directly in the theme's header template. For the React/Vite apps (TrustSeal, ScamCheck), the gtag snippet is in index.html.

Verifying the Fix

Two verification steps:

Realtime check: Open GA4 → Reports → Realtime. Open a browser and navigate from asquaresolution.com to scamcheck.asquaresolution.com. The Realtime report should show one active user, not two. The session should continue without a gap.

Acquisition report: Check the Acquisition → Traffic Acquisition report after a week of normal traffic. Cross-subdomain navigation should appear as an internal referral or — better — not appear as a new session at all. If direct traffic drops noticeably after the fix is applied, that confirms the previous inflation was caused by broken session stitching.

The Shared GA4 Property Approach

Using one GA4 property (G-MPQVF41ZYM) across all four subdomains is the correct architecture for measuring ecosystem-wide behavior. Each subdomain is configured as a separate data stream within the same property, which means:

• Cross-property user journeys are tracked as one session
• Each stream still reports its own pageviews and events independently
• The combined property view shows aggregate ecosystem behavior
• Individual stream filters allow per-subdomain analysis when needed

The alternative — separate GA4 properties per subdomain — would make cross-property analysis permanently difficult and require data blending to reconstruct user journeys.

Prevention Pattern

For any future multi-subdomain product:

1. Install the GA4 tag on all properties before any goes live
2. Configure cross-domain measurement in GA4 Admin before the first property is publicly accessible
3. Set cookie_domain to the parent domain in every gtag config call
4. Test with the Realtime report immediately — navigate between subdomains, confirm one session
5. Add cross-domain measurement to the analytics setup checklist as a required step, not an optional one

The fix takes under 30 minutes to configure. The inflated data it prevents is worth far more than that in reliable analysis.