Deduplication uses a shared event ID sent by both the Pixel and the Conversions API for the same underlying action, allowing Meta to recognize the two signals as one conversion rather than two separate ones. Without proper deduplication, running both Pixel and CAPI can inflate reported conversions and distort every downstream metric, from CPA to ROAS.
Verifying deduplication is working correctly (typically checked in Events Manager, where a correctly-deduplicated event shows both 'Browser' and 'Server' sources tied to a single event count) is a standard step in any CAPI implementation, since a broken event-ID match is one of the most common technical tracking mistakes agencies find during an audit.
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