Can we add a Functional object as a Superior SM Object in CO

Is it possible to add a Functional Object ID as a Superior SM Object , in Customer order line?

My requirement is, I need to create a Serial object when delivering customer order and that serial object should be connected as a child object under a predefined Functional object.

When Im trying the flow, I cannot see functional objects appeared in LOV of the Superior SM Object field.

It shows only the already delivered serial objects for the same customer in LOV.

Even when I create a new serial object by duplicating the previous serial object which was shown in the lov, still that doesn't appear in the LOV.

Can anyone explain the behavior.

Thanks in Advance!