I wrote my own Server Side API to send my Shopify Purchase events to my Facebook Pixel via Marketing API's Server Side API.
The problem is Shopify does not implement event_id. They also do not send the proper value for the Purchase Event (they exclude shipping price).
Can I use Server Side API event merging with out event_id?
Additionally can I get access to Event Merge on Facebook enabled on my account.
Event Merging Documentation: https://developers.facebook.com/docs/marketing-api/conversions-api/deduplicate-pixel-and-server-events#event-merging
Shopify is aware of these issues, but does not look like they'll resolve them anytime soon (it's been 2-3 years). If Facebook could contact their Facebook Pixel implementation theme, you could help get this issue resolved for all store owners of Shopify.