The spec says it should return with expand feature during the POST if we pass Prefer header in the request. I couldn’t get this working in OData v4.
220.127.116.11 Create Related Entities When Creating an Entity
A request to create an entity that includes related entities, represented using the appropriate inline representation, is referred to as a “deep insert”. Media entities, whose binary representation cannot be represented inline, cannot be created within a deep
If the inline representation contains a value for a computed property or dependent property of a referential constraint, the service MUST ignore that value when creating the related entity.
On success, the service MUST create all entities and relate them. If the request included a return __Prefer header with a value of return=representation and is applied by the service, the response MUST be expanded to at least the level that was present in the
__On failure, the service MUST NOT create any of the entities.