We need a way to link the products on a document product list so that if the items need to be changed for a changed order, when you update the contract it will also update the invoice that was generated from the contract so that you don't need to change it in two places. Currently if you update the contract and they sign again it will generate a new invoice. We need it so that if addtional items are added to the contract, when they sign again it will update the original invoice in ase they have already started making payments on the invoice that the addtional items can be added to the invoice that was already started insted of creating a new one.