The request was directed at a server that is not able to produce a response. This can be sent by a server that is not configured to produce responses for the combination of scheme and authority that are included in the request URI.
Clients receiving a 421 Misdirected Request response from a server MAY retry the request -- whether the request method is idempotent or not -- over a different connection. This is possible if a connection is reused1or if an alternative service is selected ALT-SVC.
This status code MUST NOT be generated by proxies.
A 421 response is cacheable by default, i.e., unless otherwise indicated by the method definition or explicit cache controls2.