Deduplication

Deduplication is removing the double count when the same conversion arrives twice, once from the browser and once from your server.

Modern setups send each event two ways for reliability: the browser pixel fires, and your server sends the Conversions API copy in case the browser one is blocked. Without cleanup, one sale would land as two. Deduplication spots that the two messages describe the same event and keeps only one.

The match works by sending the same identity on both copies, usually a shared event ID plus the event name. If the browser sends a Purchase with event ID abc123 and the server sends a Purchase with event ID abc123, Meta sees one purchase, not two. Miss the shared ID and your reported sales quietly double.

Deduplication only works if both copies carry the same keys. A mismatched or missing event ID means the platform cannot tell it is the same event, so your dashboard shows growth that is really just counting error.

Two pipes, one truth, or your numbers are fiction.