Having trouble uploading previous Purchase data

I am very limited with the use of ERPNext but until now, I havent had any issues with uploading Items, supplier etc until I reached purchase invoices.
I’ve been trying to upload previous purchase invoices into the system but keep recieving the message “Item Code required at Row No 1” after submitting the data sheet to the data importer.
Has anyone experienced this?

I dont believe I have to upload previous purchase orders for the invoices to be submitted.

It doesnt give me any error messages before I import the sheet, but once I click import and go back to the data importer the status is still on “not started”