preSubmitValidationsEvent (Redwood SSP Shopping Cart) — event not firing on Submit

Working in Release 26B. We're trying to implement a custom front-end validation on the Redwood Self Service Procurement Shopping Cart page to block requisition submission when lines reference more than one distinct supplier. Per Oracle's documentation, preSubmitValidationsEvent is designed exactly for this use case, but in our environment the event does not appear to fire when the Submit button is clicked, despite being correctly wired.

• In VBS, on the shoppingcart page, went to Events tab and confirmed preSubmitValidationsEvent is listed, marked "Ext Listenable," with description: "This event is raised when user clicks submit button on the shopping cart page. You can use this event to trigger custom validations as per your business needs before invoking the submit action."