This option allows you to create a order for a default supplier 1 as selected for a specific stock item (Edit → Stock items menu).

If you have selected the Documents → Create purchases on default supplier 1 on the context-menu; and no default supplier 1 have been added in the "Preferred supplier 1" field on the Stock item included in the document(s) selected stock item, an error message is displayed: 

"4L-PAINT-E Paint - Exterior
No default supplier 1 for these stock items! Please correct first!"

Click on the OK button and correct it in the Edit → Stock items, if necessary.

Note the "Supplier stock code" will be displayed in the "Item no." field of Document entry screen.