Purchase Order Approval rule

Summary:

Hi

We have a scenario where we create Requisitions and approve them. Then the buyer converts the requisitions to purchase order. The purchase order is supposed to be auto approved if there are no changes (quantity or amount). we setup the Purchasing document approval rule as below

• Is Change Order Equals No
• Document Type Equals Purchase Order
• Backing Requisition Exists Equals Yes
• Document Line total Amount in Document Currency Equals Requisition Line Amount in Document Currency

 Action:

           Action Type : Automatic

           Set Outcome To : Approved

However what is happening is that the buyer, while creating PO from REQ is able to add another line in the PO (when the PO is in Incomplete status) and the document is getting auto approved which is not correct and not desired. Seems that the system is only looking at one line (PR line) and not beyond that.