At this time the ability to set the fulfillment for catalog objects for Site Items isn’t currently available. The Catalog API will create items that will be in the Square catalog that you can bring into the Square Online Store and set the fulfillment.
That’s really disappointing. I have nearly 600 items and it sounds like I have to go to each one and update the fulfillment options by hand. Is that correct?
If so, is there a way to make a feature request for the APIs?