How to Firm Purchase Orders from Supply Plan?

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In supply Planning in Supplies and Demands table we can change the firm status of already collected Purchase Order from Not-Firm to Firm.

But when I make the changes and try to mark the Order for release I'm unable to do so.

How can we mark the PO's as Firm from supply plan and then release it so that in the Procurement also the PO schedule is updated indicating that the schedule is firmed.

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