How to Fix Duplicate Events Between the Meta Pixel and Conversions API

Running both the Meta Pixel and the Conversions API is best practice — but if they aren't deduplicated correctly, Meta counts the same conversion twice. Your reported numbers inflate, your cost-per-conversion looks artificially good, and your optimization suffers. Here's how to fix it.

Why duplicates happen

When you send an event from both the browser (pixel) and your server (CAPI), Meta receives two events for one real action. If it can't tell they're the same, it counts both. Deduplication is how you tell Meta “these are the same event — count it once.”

How deduplication works

Meta matches the browser and server events using two things:

• A shared event_id — the same unique ID sent on both the pixel and the server event for a single action.
• A matching event_name— e.g. both are “Purchase.”

When both match, Meta collapses the pair into one event. When the event_idis missing or different, it can't — and you get duplicates.

How to fix a high duplicate rate

1. Generate one event_id per actionand use it on both the pixel and the CAPI event. Don't generate a new ID separately for each.
2. Send matching event names on both paths.
3. Verify in Events Manager.The event details should show events as “deduplicated,” and your duplicate rate should fall.
4. Watch after every site change. A deploy that alters howevent_id is generated is the most common way deduplication silently breaks again.

Why it's easy to miss

A rising duplicate rate doesn't break anything visibly — it just quietly inflates your numbers, which can even look like betterperformance at first glance. That's what makes it dangerous.

Catch duplicate spikes automatically

Taglert tracks your duplicate-event rate across every connected account and alerts you when it spikes — so you can restore the sharedevent_id before your reporting drifts. See our guide on running the pixel and CAPI together for the full setup.