It’s been a while, but when I ran FB ads to an s2 site I did something similar to what
uurayan said above.
That code would need the normal pixel loaded earlier in the page to work and since FB changes all the time it’s probably different now, but it’s a good starting point. I really don’t know because I don’t use FB ads anymore.
Look at the FB pixel docs, make sure your pixel is loaded first, and put whatever they suggest for a conversion event later on the page (putting in api/tracking as suggested above, for example).
It’s more of a FB and JS question once you know that s2 wants code like this in api/tracking.
And, as far as I can remember, I think there are sections to track different accounts (even free ones) there.
s2 actually make it much easier to implement than even WooCommerce. If you’ve ever worked with MS Ads, then you’ll know