Currently Shopify doesn't allow you to manually fill a product when there's a fulfillment service option. So what do you do if you want to manually fulfill an order for a product managed by Slingshot? Let's say for example you have inventory on hand, for a brand loaded into your store by Slingshot.

Step 1.

Step 2.

Step 3.

Once that's done you should have the option to toggle between locations, getting both the option to fulfill from your location, or send request via Slingshot.

This process may change in the future.