Developers can design a wide variety of solutions using Shopify's Fulfillment Orders API to facilitate fulfillment for merchants. Third-party warehouses that pack and ship orders, print-on-demand services, and label printing and fulfillment are common requirements from merchants that Shopify's Fulfillment Orders API supports.
There are two main ways to build a Fulfillment app with Shopify:
Order Management App
Order management apps can fulfill orders on behalf of merchants. Apps can automate fulfillment, or merchants can directly fulfill orders through the app. Order management apps can help merchants with complicated shipping workflows that include multiple steps like buying shipping labels, reassigning inventory based on availability, or rescheduling upcoming shipments for a different date.
If your app doesn't directly manage the distribution of physical inventory in warehouses, you're likely building an order management app.
Fulfillment Service App
Fulfillment service apps are services that perform the fulfillment of physical products for merchants. Workflows exist through the Admin and the API that allow merchants (and other apps) to submit requests to fulfill orders. These fulfillment services can subsequently approve or deny requests to fulfill. Once a request is approved, merchants can also submit requests to cancel the fulfillment before the order is shipped.
Fulfillment service apps allow for high-quality communication between fulfillment centers and merchants and transparent reporting about order status through the Shopify Admin.