The idea would be you add the barcode into that field.
But honestly I think header won’t support {ITEM TAG:Barcode} like I said in a previous post. I had a similar problem myself in the past.
Actually what are you trying to accomplish? Is it you want to show item number on each button? like this:
If so, I wrote a guide how to do it here - you just need to store your item number (set product tag to “Item Number”) then run the SQL script. Check further down the page and there is details how to set the SQL script as a database task.