# HTTP 421 Misdirected Request

**Code:** `421` · **Category:** HTTP · **Seen on:** REST API

The request reached a server that isn’t configured for that host name — usually HTTP/2 connection reuse across domains sharing a certificate, or a wrong SNI.

## Meaning

With HTTP/2, browsers reuse one connection for several hosts covered by the same certificate (e.g. a wildcard). If those hosts are served by different backends or virtual hosts, the server replies 421 so the browser opens a new connection.

Apache also returns 421 when SNI and the Host header don’t match, and reverse proxies return it when proxying to an HTTPS backend without passing the right SNI.

## Common causes

- HTTP/2 connection coalescing across hosts on a shared/wildcard certificate
- SNI and Host header mismatch (Apache SSLStrictSNIVHostCheck)
- Proxy forwarding to an HTTPS upstream without proxy_ssl_server_name

## Quick fix

1. Give each host its own certificate, or serve them from the same vhost/IP
2. Nginx proxying HTTPS: enable proxy_ssl_server_name on
3. Check vhost ServerName/ServerAlias for the host

## Detailed fix by platform

### Nginx

1. 

```nginx
location / {
    proxy_pass https://backend.example.com;
    proxy_ssl_server_name on;
    proxy_set_header Host backend.example.com;
}
```


### Apache

1. 

```apache
# per vhost: ServerName and matching certificate; or relax strict SNI
SSLStrictSNIVHostCheck off
```


## How to diagnose

1. **Hosts** — Which hostnames share the certificate/IP?
2. **SNI** — openssl s_client -servername host -connect ip:443
3. **Proxy** — Does it send SNI upstream?

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Source: [WhatIsMyError](https://whatismyerror.com/errors/http/421-misdirected-request)