I am having trouble with marking invoices as paid. I know I can create a custom field with a picklist of Paid and Unpaid but that seems elementary when working with invoices in excess of tens of thousands of dollars. 

   We frequently take partial payments from customers too. So determining how much is owed on an invoice is important as well. This is important for reconciling accounts receivable. I thought about using the "Adjustment" category but unfortunately that is already being used as a shipping line. Is there a way to add another line that acts just like adjustment does. That may work for me. 

   Any help is greatly appreciated.