Manage of server error response with backbone

I would like to know the best way to manage server error response on new, update or delete models. At this moment the server returns a http status code # 400. But the default error handler in Backbone is not showing the errors.

How can i show these errors?

Is it ok that the server returns http error headers when a server side validation fails? (Maybe is better return a success response with a status='ERROR' message)