Question

We migrated our conversion tracking from Google Analytics UA to GA4, and now conversions in Google Ads are down 40% while Shopify sales are unchanged. Has anyone else seen this attribution gap with GA4?

Answer 1

Yes — you're not alone. Many advertisers have seen this exact issue after migrating from Universal Analytics (UA) to Google Analytics 4 (GA4). 

The drop in Google Ads conversions (despite stable Shopify sales) usually comes down to differences in attribution models, event setups, and data sharing between GA4 and Google Ads.

Here's why you're seeing a 40% drop:

1. Attribution model mismatch

• UA defaulted to Last Click.

• GA4 uses Data-Driven Attribution (DDA) by default (if eligible), or Last Click if not.

• DDA in GA4 may attribute more conversions to organic, direct, or referral sources instead of paid ads.

Fix: In Google Ads, go to:
Tools > Conversions > Your GA4 conversion > Edit settings > Attribution model
Choose Last Click temporarily if you want to align more closely with UA’s historical reporting — or ensure your expectations match the DDA model.

2. Not all Shopify events are firing as GA4 conversions

• You may be tracking purchase events in Shopify, but if GA4 isn’t configured correctly to count those as conversions (via Tag Manager or direct integration), it won’t reflect them in Google Ads.

Fix:

• Verify purchase event is tagged as a conversion event in GA4 (under Admin > Events > Mark as Conversion).

• Double-check that the event includes all necessary parameters (currency, value, transaction_id).

• Use Google Tag Assistant or DebugView to confirm proper firing.

3. Missing GA4 to Google Ads linking or enhanced signals

• If your GA4 property isn’t linked properly to Google Ads, or enhanced conversions/signals aren’t enabled, conversions won’t import fully.

Fix:

• Recheck under GA4 → Admin → Product Links → Google Ads → Confirm bidirectional linking.

• In Google Ads: Go to Tools > Conversions > GA4 event > Ensure it’s marked as "Primary" and importing properly.

• Consider enabling Enhanced Conversions for Web via GTM or Shopify if not done already.

4. Conversion windows and lookback windows differ

• GA4 and Google Ads may use different lookback windows, so conversions may appear later or be missed in reporting.

Fix:

• Align lookback windows (default is 30 days; verify in GA4 and Google Ads).

Until GA4 and Ads stabilize for you, consider running both UA (if still active) and GA4 side by side, or use Shopify’s backend sales as the “truth” while troubleshooting. You can also refer these for GA4 queries.