Tracking Cost of Goods Sold

Site URL: http://www.shophomework.com

For accounting purposes I need to track the cost of goods I sell. My brick-and-mortar POS allows me to do this, but unfortunately Shopkeep and Squarespace do not communicate. I'm considering leaving Shopkeep and doing future brick-and-mortar sales through the Squarespace POS, once we're allowed to reopen, but I really need to be able to track cost of goods. If Squarespace can't do this, is there an extension that can?

I'm attaching a screenshot that I hope will help clarify what I'm looking for. 

Thank you! I'll do that.

can a product cost field be custom coded?

Have you solved this with the aid of any danger? I am lost and can not get this proper? Any developer that i can pay him money to get this right here.