What HTTP status response code should I use if the request is missing a required parameter?

Question

I am thinking 412 (Precondition Failed) but there may be a better standard?

Answer 1

I Usually go for 422 (Unprocessable entity) if something in the required parameters didn't match what the API endpoint required (like a too short password) but for a missing parameter i would go for 406 (Unacceptable).