Allow Item Substitution Checked on TO Line but Unable to Pick Substituted Item at Pick Confirm

Summary:

In PIM, relationships have been set up between item X with Y as a substitute in both source & destination organization.

Source Org is APX & Source Subinventory is APXWIP. Destination Org is APY & Destination Subinventory is APYWIP.

In Inventory Organization Parameters for both organizations, 'warehouse accepts item substitutes' is checked so 'Allow Item Substitution' is auto checked upon Transfer Order creation.

However, TO gets created for Item #: X with 60 qty when 40 is on hand in Source Org is APX & Source Subinventory is APXWIP & on hand is available in Y in Source Org is APY & Source Subinventory APYWIP for the remaining 20 qty - there is no option to select the item substitution during pick confirmation.