I found a place on Shopify where I can ask a question (https://help.shopify.com/en/search/01hcg3y7ezk0kern7eysm39g9p ). when I asked, “fulfillable_quantity = 0”, it responded with the following: “When the fulfillable quantity is 0 in Shopify, it means the product is out of stock. Shopify won’t allow customers to purchase that item until you adjust the inventory levels. More info here.”
The issue is client may have subscription orders or want to do preorders. Also, some products may be “Kitted on Demand”, therefore no inventory exists at the warehouse ahead of time. If an order exists, we need to know the fulfillable quantity (quantity - minus any refunds (etc.)) independent of what the current Inventory level is. Inventory level should not affect the fulfillable_quantity sent on an order either thru the API or webhooks. At best, inventory level should prohibit new orders from being placed from the store for those items, and that is it. Once the order is, created inventory level shouldn’t affect what is returned.