Setup -> Rules -> Security -> Processing Constraints

Application: Order Management
Entity: Order Line
Operation: Update
Attribute: Request DateUser
Action: Require Reason and Require History
Scope: AnyValidation
Entity: Order Line
Record Set: LineValidation
Template: Entered
Applicable To: All responsibilities

I am expecting a prompt for Reason Code if I update the Request Date field in Order Line. It works for my existing responsibility but NOT for my new responsibility that tied to my new Operating Unit (OU).

At OM setup, System Parameter Value, select the new OU, Generic Parameters category, Audit Trail parameter, the initial value was blank. Now, set it to "Enable when Order is Booked". The window for Reason Code will appear after you updated the Request Date and Save.