During your sync operation, you receive an error showing, Line item ‘xxx’ fulfilled on target application, which is Shopify here.

Cause

Multiple line item in the order fulfillment process is already fulfilled. 

Resolution

The error can be resolved as given below:

An order line item fulfillment requires an acknowledgement to the source to ensure the same line items are not picked up again and again. Your order fulfillment for this sync operation encountered a line item which is already fulfilled. You must ensure the fulfilled order status is updated to source application before next sync iteration. Order status can be updated using the following process: 

• Store Shopify fulfillment id in source application
• Use a flag to identify already fulfilled order in source application

  You can refer to Integration Strategies Best practices for further understanding. 

Do you know how to automate your Shopify store and streamline your business? Check this out now: Automate Your Shopify Store Easily