Hi @KellyWorrall,
Thanks for the question! That may be a question for Facebook Conversions Support if you also have lead events being sent directly with a thank you page submission.
If there are going to be duplicate events sent from the Zap to Facebook and directly from the thank you page to Facebook, you may be able to deduplicate those events.
Documentation from Facebook, referring to how to deduplicate events: https://www.facebook.com/business/help/823677331451951?id=1205376682832142
From Facebook: "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."
Hope that helps!