GA4 audit: find out how much revenue your analytics is missing

A DTC store came to me because their GA4 purchase numbers never matched Shopify revenue. GA4 showed 60 purchases a week. Shopify showed 100. The difference was not bots or returns - it was tracking gaps.

The root cause: their GA4 setup used Shopify's native Google channel integration. That integration fires a purchase event when the thank-you page loads. It works on desktop, standard browsers, no checkout extensions. It breaks on Shopify's hosted checkout when the user pays via Shop Pay, when they are on a mobile device with aggressive ITP, or when the thank-you URL loads in a context the gtag snippet cannot reach.

Result: 41% of real purchases never appeared in GA4. Every campaign decision - budget allocation, creative testing, audience targeting - was based on a sample of 59% of conversions. Not a representative sample either. The missed conversions were systematically skewed toward mobile and Shop Pay users.

The fix was server-side purchase events fired from the backend, deduplicated by transaction_id against any browser-side events that did fire. Three weeks from audit to 100% capture rate. No more gap between GA4 and Shopify.

I start with the numbers before I touch any code. GA4 purchase count vs platform revenue for the last 90 days. If the gap is under 5%, the problem is probably elsewhere. If it is over 10%, the checkout tracking is broken.

Then I go into the implementation: Google Tag Assistant, DebugView, network traffic on the checkout flow. I walk every step with a test transaction in a staging environment where possible, and a real low-value transaction where not.

I document every finding with: what is wrong, where the break is, what a correct implementation looks like, and effort to fix (hours, not story points). You get a prioritized list you can hand to a developer or have me implement.

The most common findings in order of frequency: checkout page purchase event missing, duplicate event firing (browser + server both firing without deduplication), missing item-level parameters on purchase events, incorrect conversion event marking, and attribution window mismatch.

A GA4 audit is often the entry point to a broader marketing attribution engagement. Once GA4 is accurate, you have a foundation for cross-channel attribution - reconciling GA4 data with Meta CAPI, Google Ads enhanced conversions, and your CRM.

If the audit finds server-side tracking gaps (it usually does), the next step is a server-side tracking implementation. If you want a broader picture of all your measurement gaps at once, start with a tracking audit that covers all channels simultaneously.

Not sure GA4 is the problem yet? Run the free growth leak audit first: it reads your tracking layer from the outside and shows which dimension is actually leaking.