It is such a convoluted and unclear process but this was instrumental to me figuring it out in the end - Thank you kc2615!
In squarespace under Marketing> Facebook Pixel & Ads - this section and the information there is what syncs everything together.
You need to copy and paste the Facebook pixel ID from facebook commerce manager into squarespace and click save.
Back on facebook in the catalogue section > Data Sources > Add New Feed
You need to take the squarespace url link directly below Facebook Pixel ID and use this as the url in the feed to upload.
No coding necessary. Still a headache figuring it out....