421 Misdirected Request
The request reached a server that cannot answer for this host.
What it means
Happens with HTTP/2 connection reuse across hostnames that share a certificate.
What your client should do
Retry on a new connection.
Should you retry?
Yes, with exponential backoff and jitter, and only for idempotent requests (GET, PUT, DELETE) or requests protected by an Idempotency-Key.
Try it
The free practice API returns this status on demand, with the headers a well-behaved API would send. Call GET /api/play/status/421 from Endpoint Client and open the Explain tab.
Defined in RFC 9110. All status codes and headers