Fulfillment Service - Inventory Management

Shopify Partner
13 0 2

I've set up a fulfillment service through a private app. I want to use this service for inventory management. Currently, I'm having to push products into shopify individually to sync their inventory with our system in-house. However, using a fulfillment service allows me to sit back and wait for Shopify to ask my app what the stock level is for a certain SKU, perfect!

However, I don't want the orders to be fulfilled by my app. I still want to be able to ship things through Shopify. Is this possible? When changing the inventory_management field on the Product Variant object through the API, I get a 422 error, unless the fulfillment_service property is set to the same handle. This is in-line with what the docs say (https://shopify.dev/docs/admin-api/rest/reference/shipping-and-fulfillment/fulfillmentservice?api[ve...)

But I would like fulfillment_service to be 'manual' and inventory_management to be the handle of my app. 

Also, when I change my fulfillment_service of my items, I lost the functionality to use In-Store Pickup in my app. Potentially this is a bug? Not sure why a fulfillment service would prevent in store pickup. 

Any insight would be greatly appreciated.