How can we auto fill the PO DFF with the negotiation number when generating a PO from a negotiation?

Currently, the system behavior on the Purchase Order side differs from that of the negotiation process. When a PO is generated from a negotiation, there is no direct linkage field on the PO header that stores the originating negotiation number. Business users have requested that a Descriptive Flexfield be created at the PO header level to capture this information. The DFF should be automatically populated with the negotiation number at the time of PO creation from the negotiation, ensuring traceability and consistency between the negotiation and PO records without requiring manual entry.