How to make 'Justification' field mandatory on PR headers only for Punchout PR in RSSP

Summary:

There is a requirement where we have to make the 'Justification' field on the purchase requisition headers screen mandatory only when it is a punchout requisition. For any other requisition it should not be a required field. How can we achieve this on the RSSP screen?

Content (please ensure you mask any confidential information):

There is a requirement where we have to make the 'Justification' field on the purchase requisition headers screen mandatory only when it is a punchout requisition. For any other requisition it should not be a required field. How can we achieve this on the RSSP screen?