Hey @Shopify_Wal_App , no worries, happy to help!
Calling fulfillmentOrderClose after you partially fulfill wouldn’t create a new Order or automatically change the Order quantities.
Basically, it marks the remaining 2 units on that FulfillmentOrder as incomplete and returns control to the merchant. The order still shows 3 fulfilled and 2 unfulfilled. If the merchant later re-requests fulfillment for the remainder, Shopify will create a new FulfillmentOrder at that time; otherwise they can reassign or refund. If the merchant wants those 2 units “canceled” (i.e., removed/refunded), that’s done via order edits/refunds, not by fulfillmentOrderClose. Hope that makes sense, let me know if I can clarify anything further as always!