SFS now supports capturing and mapping external Item codes during packing. Please follow the below steps:
Go to the Packing screen in the Outwards section.
Click on Configurations
Enable the configuration Capture external Item Id in pack by Picklist ID/Order ID.
To pack orders using Picklist ID, please scan External Item ID after scanning Picklist ID and Client SKU ID.
To pack orders using Order ID, please scan External Item ID after scanning Order ID and Client SKU ID.
Please verify External Item ID before mapping to Client SKU ID, as it's irreversible.