Introduction
After working with SAP for more than 15 years and travelling across the Globe for SAP Projects one enhancement I always use to build is to make sure the Buyer cannot buy more quantity than Released in the Purchase Requisition.
After sometime I got tired and said there should be an easier way to do it and guess there is a very easy way which will Cost the Customer nothing.
Problem
Purchase Requisition Approved amount.and PO Ordered Quantity
Solution
Go To Transaction Code OLME

Click as Mentioned Below

Now Click New Entries

Now Enter the following Entries and Save it.

Now we have only 15 Open quantity that can be used from the PR

Now we try to buy more than the Open Quantity available in the PR and Wala we got the Error. We did this without ABAP Coding.

Conclusion
In SAP there is always a better solution available if you have the urge to explore.
Here is the Video Version
https://youtu.be/igOQjLBDtdw