Yes, I have tried this one, but it does not solve my requirement. What I am looking for is dependency between two custom fields (no need for item mapping at all). Let say I have fieldA and fieldB. FieldA get its choices from an endpoint and user can select. Then the choices for fieldB (to be provide by another endpoint) is dependent of the choice made by the user for fieldA.
So, no need for incoming or outgoing item mapping. Just two custom fields that depend on each other.