POS Saved Carts (Draft Order) attribution

We are looking to be able to attribute a draft order to our retail locations. Currently we are sending Draft Orders from the POS. We want to be able to understand the CVR and which locations are driving those sales. There isn’t a way to add a tag in the POS so looking for a way to be able top add a tag via Flow or similar but not seeing any data points that might help with this.

I think the Flow action you’d want is Update draft order metafield, but I’m not sure how you’d trigger it, since it’s originating from POS.