Just wanted to follow up here to confirm that Facebook uses the Event ID and name for deduplication. Their documentation states “After you set up the event name and event ID parameters, we deduplicate all but the first event we receive if the events have the same event ID, have the same event name, are received by the same pixel ID and are received within 48 hours of the first event.” - About deduplication for Facebook pixel and Conversions API events
The event ID will need to be a unique ID. So in cases where your Zap is triggering more than once for the same order, you’ll want to ensure that the Event ID field in the Facebook Conversions step is set to be a unique value, like the Order ID from the Shopify trigger step. This will help Facebook to identify whether the conversion is a duplicate event.
And to prevent the Zap from sending duplicates through to Facebook in the first place, you’ll want to follow the suggestions on the thread Danvers linked to above in order to set up some deduplication for the Zap. We also have another article on stopping duplicate triggers that may be helpful: