Doctype issue field

hello i have this following problem,

i think it’s right to write item.barcode but it’s not working it’s saying invalid link options doctype
another solution was this one

but still in the barcode section it shows me the item code with the item name but it doesn’t dropdown the item barcode, i don’t understand why

What you are trying to do?

Show barcode below the item name when you select an item?

i’m trying to make a dropdown barcode so i can show the barcode when i click on the field but it’s not working,
unlike in the table on the exchange item name it works it shows a dropdown of the name and code.