I absolutely agree with you on @SQUARESPACE being useless in this situation.
I've tried everything and still can not get the product tagging to work. I've deleted and re-uploaded my products. Made a whole new catalog, etc. I've attempted several times and finally gave up after finding this forum post and realizing it's not my fault.
What's really frustrating is the pointing of fingers. Squarespace has the ability to reach out to FB and IG and work through this to streamline it. Clearly those companies are capable of working together to solve issues like this. So why don't they?
At this point I am feeling like everyone dealing with this should get a 40% refund on their purchase, since this feature is highly useful and one of two reasons I chose Squarespace.
Ugh.
I'm running into this issue as well. What I've noticed is the information squarespace sends to Facebook doesn't even include the column "inventory" or "stock". There is an "availability" column which tells Facebook that the item is available, but nowhere in the SS data does it give the quantity. It was extremely frustrating and time consuming to track this down.
Additionally if you export your inventory... it DOES have the information. Why in God's green earth would they send a different spreadsheet through the provided link than the one you get when you download your inventory CSV. I looked at the link behind the export button thinking maybe I could use that, but alas..it fails.
SS should update and item the inventory column to the provided feed, or simply use the same spreadsheet from the export button in the inventory tab.
I need this solution asap 😕