PO Number in Vendor Downpayment - Message Control

Dears

We have a requirement to enter the PO number in the line item while entering vendor down payment using F-48 transaction.

We cannot make the PO order number in the F-48 mandatory. However, if the PO number is not entered by the user,

a warning message should be issued to the user that PO number is not entered.

Can we control it through changing message control ?

Please advise.