When invoicing a receipt in POP, this customization will check the previous quantity invoiced and the quantity returned for the line item. The maximum quantity allowed to be invoiced is based the following formula: Quantity Shipped minus (Previous Quantity Invoiced plus Quantity Returned). This customization will not allow invoicing of more than this amount.  If this is the tool you need, then you may use the attached file.  Please unzip the file from the link above and read the PO Returns 10 word file for the install instructions.