The 421 (Misdirected Request) status code indicates that 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 reused (Section 9.1.1) or 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 controls (see Section 4.2.2 of [RFC7234]).