Modify Invoice Script Code

I have an invoicing script that was written by another freelancer, and it is incomplete. There are a few areas that still need development in order to have this module in full working order. I am happy to provide the details of what is not currently functioning within this module. Should be an easy fix/implementation for a skilled programmer. The included files outline the process of adding invoices, adding dynamic line items to each invoice and then keeping invoices organized to each folio. (ie. a folio will have multiple invoices within it.) The problem is that only certain parts of data write to the DB, and some of the writes are incomplete so they do not link to the appropriate invoice for the folio, or they dont list at all.) When I look into the DB side of things I can see the incompletes, the code however has progressed beyond my level of easy comprehension; I believe with a little guidance on my part for what we want this should be an easy fix for a good programmer. I am available to assist in walking through the backend to define the areas that are not working to spec. Here are the specifics about what is not working correctly: 1) When an invoice is added, its not carrying over the IDs correctly to link it to the folio, so when you goto manage the invoices for a folio, you dont see them listed. 2) The credit/debit section of the invoices, upon saving an invoice is not writing the "total" back to the database.(ie. plAmount) 3) The datepickers for the ledger line items are not working correctly.