You can check the data we pass to Facebook in the app dashboard by selecting the logs section.
This shows the Purchase events we actually pass, including the data with the event, and that Facebook has acknowledged receiving.
Please note that there are many reasons an event may not show in Facebook, for example if a user opts out of tracking or has used a private/incognito browsing window and you should expect to gather 20+ purchases before a pattern emerges
This functionality is provided so that you can cross check the Purchases you have made in your Shopify store with the data and events that has been passed to Facebook. However, it is no guarantee that Facebook with display that data or in what form.