Why is my Meta Pixel showing a “De-duplication error” for standard events?

A Meta Pixel de-duplication error is triggered when your server and browser event names, event IDs, or external ID variables are missing or misaligned, preventing Facebook’s backend from identifying matching event pairs.

“The usual culprit is an event ID or name that doesn’t quite match between your browser pixel and your server event. I’ll line them up and clear the error within 24 hours for $99.”
— Jeff Bollettino, Managing Director, Ignite Conversions