Copy paste as follows:
Do not change the headings:

This may be the Item’s Legacy Code in Streamline.

Alternatively, this may be your Customer’s own SKU (Go to the Customer’s Item Catalogue, Edit and populate).

NB: the Customer’s own SKU may also be displayed in the Customer’s Packing Slips (Delivery Notes) and Invoices. [ Distribution > Settings > Packing Slips ]
[ Finance > Invoices > Templates ].

You must create these in
[ Customer > Edit Address ].

Or [ Batch Edit > Customer Addresses ] display Customer Code Column.