During your sync operation, you receive an error which says ‘Order no longer exist’ in the target application, which is Magento 2.

Cause

There might be a number of reasons for this error:
a. Order is deleted in Magento while updating from the source application for synchronization.
b. Update Process is executed before order creation.

Resolution

To resolve this issue, follow the links below for reference.

• Check weather the Order exists in Magento before running the synchronization with any dependent data.

         Refer Order Creation in Magento.

• Check weather the syncback touchpoint is executed or not.