Meta Ads Manager

Meta deduplicates redundant events when the browser and server send identical event_name values plus either the same event_id or the same external_id + fbp pair, all to the same Pixel ID inside a 48-hour window^[1]. Outside that window, both events are kept, so a delayed server-side fire after a connectivity issue will still be counted twice^[2].

The recommended setup is to mint a single unique event_id per user action server-side, then pass it to the browser via the eventID field on fbq('track', 'Purchase', {...}, {eventID}) and to the server via event_id on the Conversions API request^[3]. Both events must also share an identical event_name; spelling drift between Purchase and purchase defeats the matcher^[4].

Verify the result in Events Manager under the Event Deduplication tab - the Rate of Events Deduplicated should sit between 50% and 80% for a healthy redundant setup, with Overlap > 60% indicating the dedupe key is reaching both sources^[5]. Lower numbers mean a server-only or browser-only segment is leaking into the dataset.

For app events, the same event_id + event_name logic deduplicates Conversions API events against SDK/MMP events^[6]. Cortex's CAPI Sentry checks the Dataset Quality API daily and flags any Pixel where deduplication rate falls below 50% or Event Match Quality score drops more than 0.5 week-over-week^[7].