Tracking purchases from specific /subsites even when all purchased from same shopping cart

Hello! My company is doing co-marketing partnerships with numerous Chambers of Commerce in the US.

Each Chamber is getting their own sub-site on our website called www.OurWebsite.com/ChamberName.

Each Chamber will tell their members to go to their specific sub-site to order the product.

Obviously, all of those sub-sites route to the same shopping cart.

How can I see which orders originated from OurSite.com/Chamber1 vs. OurSite.com/Chamber2 vs. OutsSite.com/Chamber3, so on and so on?

We need to keep track of this because we have to give a report to each Chamber of how many of their specific members ordered product and which product they ordered. 

Thank you so much Squarespace Community! 

Anyone have any answer here? I'm trying to do the same thing.