Maybe for non-English speaking people, "Demand order" and "Supply order" can have the same meaning.
"Demand order" can be read as "an order for a request, a demand, of goods", and "Supply order" as "an order to receive a supply": i.e. they can be the same thing.
If I remember well the mechanics, maybe could "Supply order" be better expressed as "Supply offer", or even better turn "supply" into "exportation"? So, it is clear that a site allows to supply that item.
And if the site serve as a deep space depot, it could have demand and supply active together: to receive goods from producing locations and distribute them to other places.