Add custom table field to invoices

I need to create a custom field that mimics the line items table.
It only needs to be a table of about 3x3 of basic text fields.
How do I create this and then add it to the invoices module?

Hi there,

You would need to mimic/replicate how line items are generated for Quotes and do this for invoices, and then modify the code.

This is not a simple change and needs an understanding oh js/php/sugarcrm.