I worked with a client where everything looked fine: GA4 collected events, Meta and TikTok pixels were set up.
But when we compared conversions, it didn’t add up: Meta showed 50 purchases, GA4 showed 80, CRM had 110.
Wow...
But wait... All events were sent from the browser — and the browser is unreliable.
Here’s why:
• AdBlockers, iOS, Safari’s ITP block tracking requests
• Users leave before the pixel fires
• Platforms don’t confirm event delivery — if it’s dropped, it’s gone
• Purchases are recorded differently in GA4, CRM, and ad platforms
• Some events (e.g., page_view) might go through, while key ones like purchase silently fail
Without server-side, you can’t see what’s missing - and you can’t fix it.
In this case:
• Platforms undercounted real events - so optimization skewed toward wrong users.
• High-performing creatives got buried — because Meta didn’t see the purchases.
• Reports across GA4, CRM, and ad accounts never matched - so decisions were made on “the cleanest chart”.
• Budget shifted away from what actually worked - because browser-based tracking failed silently.
GA4 didn’t raise a flag. It just stayed quiet when data got lost.
Now I always recommend GTM Server-Side for serious paid traffic. Why?
• Events go from your server — no AdBlock (yes, there are some exceptions).
• You control what gets sent, how, and when
• You can standardize events across GA4, Meta, TikTok, etc.
• You get logs, confirmation of delivery - no more guessing
• You see what was accepted - not just what was fired
If platforms don’t receive clean data, they can’t optimize. And if they optimize on garbage - performance dies quietly, one invisible event at a time.
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