Copy paste as follows:
Do not change the headings:
CSV Template
Item Legacy Code
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 ].