Why are some events deleted by Facebook (event deduplication)?

The pixel and Conversions API let you share standard and custom events with Facebook so you can measure and optimize ad performance. As a reminder, the pixel lets you share web events from a web browser, while the Conversions API lets you share web events directly from your server.

If you connect the activity of your website using both the pixel and Conversions API, Facebook may receive the same events from the browser and the server. If such redundancy is detected, then Facebook can choose to keep one of the two events and delete the other. This is called deduplication.

For example, one purchase can be reported once by the pixel and once by the Conversions API. Without deduplication, these two deliveries could be counted as two purchases even though only one purchase occurred. Deduplication helps prevent this double-counting.

To recognize two deliveries of the same event received for the same pixel, Meta compares the event name (for example Purchase or AddToCart) and the event ID. The module uses a shared ID between the pixel and the Conversions API for the same event occurrence sent through both channels. The browser sends this ID as eventID; the API sends it as event_id. The name and ID must match between the two deliveries; separate occurrences must have separate IDs.

Deduplication lets Meta count one occurrence for the two corresponding deliveries. It does not mean that an order has been deleted from your shop. To check the deliveries, review the events received in Meta Events Manager and compare their names and IDs. Read Meta’s help on verifying deduplication.

Read Meta’s documentation on deduplicating pixel and Conversions API events.