My name is Michael, I’m a Guru here with Shopify, thanks for getting in touch. :)
There's no need to add any additional code once you added the Pixel ID to the Online Store > Peferences Section of you admin. You can see a guide on setting that up here.
I hoep this helps and best of luck with your Business going forward! :)
Hey Joseph, to add to Michael's post, if you have this setup already but you're not seeing the info in FB Ads Manager, you might just have to enable the column in Ads Manager.