Add foreign_trade_details to sales invoices

I am trying to add foreign_trade_details (from item) to sales invoice as the option is not there in the items table.

i created a new field (hs_code) and in the fetch from added (item.foreign_trade_details) as item is already linked, but I cannot seem to be able to fetch it.

any advice, please?

Got the solution:

If the field type you are linking to is ‘LINK’, you need to add it as a ‘link’ in the new custom field as well.