Admin v1 is rather inconsistent when it comes to how child resources are handled. Some examples:

• Creating a user with a list of mapped roles - the roles are just completely ignored
• Creating a group with a list of mapped groups - groups are mapped if found, otherwise an error occurs (500, but should really be a 403)
• Creating a client with a non-existent default client scope - default client scope is ignored, and filtered (should be a 403 really?)

There's plenty more examples, and I'm sure any possible result can be observed from different endpoints in Admin v1 (children being created, children being ignored, children being silently ignored if not found, 500 status codes, etc.), and I'm also sure sometimes a resource can be created with child resources, but not updated with child resources.

End of the day we need consistency here; and if creating a resource doesn't support including child resources then the OpenAPI docs should not list is as such (suggesting maybe there could be a create UserRepresentation, and a different UpdateUserRepresentation, or whatever).