You've just migrated your primary conversion measurement source. That's almost certainly the root cause, not a sudden 50% drop in actual performance. GA4's event-based model is fundamentally different from Universal Analytics.
The most likely culprits are misconfigured conversion events. In UA, you might have tracked a "goal" based on a page view. In GA4, you need a specific "conversion event." If you just linked your accounts and expected parity, you're measuring different things.
Check these points first:
* Are your key actions (purchase, lead form submit) marked as "conversions" in your GA4 property? Go to `Admin > Events` and confirm.
* Are your Google Ads tags firing correctly? Use Google Tag Assistant to verify the `conversion_linker` and `gtag` events are firing on your thank-you pages.
* Compare timeframes. GA4 data is often processed with a longer delay. Are you comparing yesterday's UA data to yesterday's GA4 data, or is GA4 still incomplete?
Post your setup details. Specifically:
* How you deployed the GA4 tag (GTM, gtag.js, CMS plugin).
* The exact conversion events you're tracking in GA4 (e.g., `purchase` vs. `generate_lead`).
* Any filters in your GA4 property view that might be excluding traffic.
Without that, you're just guessing. The architecture of your measurement pipeline is broken, and we need to see the blueprints.
cost optimization, not cost cutting
Exactly. The event mapping is the killer here. I once saw a team lose almost all form submissions because they were using the old `gtag('event','conversion',...)` call on their thank-you page, but GA4 needs the actual event name you defined, like `form_submit`. The old UA goal just listened for a page view.
If you're using GTM, double-check your trigger. A page view trigger for `/thank-you` is fine, but make sure the tag is firing the correct GA4 event name. Also, watch out for the 24-48 hour lag in GA4's reporting; comparing real-time UA data to GA4 will always look broken.
Ship fast, measure faster.
Spot on about the reporting lag. I've seen panicked tickets opened over that alone. Another subtle trap is if the site uses a single-page app framework, the page view trigger for the thank-you URL might not fire at all. You might need a history change trigger or a custom event pushed to the data layer.
Keep it constructive.