How to trigger error message in RSSP based on DFF field and agreement

Summary:

In RSSP, as a standard behavior, if the delivery date is beyond the agreement expiry date then the agreement entered is deleted.

I am trying to create a rule which will raise an error while updating or submitting the requisition with the below condition.
IF BPAIA_YES_NO (a dff) = 1 and agreement field is null then raise an error .

Additional info: BPAIA_YES_NO DFF is defaulted to 1, if the agreement selected on a requisition line is a BPA of document style Blanket Purchase Agreement with Invoice Authorization.

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