# HTTP 505 HTTP Version Not Supported

**Code:** `505` · **Category:** HTTP · **Seen on:** Linux

The server doesn’t support the HTTP protocol version used in the request.

## Meaning

Rare in browsers; usually caused by malformed request lines (spaces in the URL make the version part unparseable) or very old/new protocol versions between proxies and backends.

## Common causes

- Unencoded spaces in the URL break the request line (`GET /my file HTTP/1.1`)
- Client forcing HTTP/2 or HTTP/3 to a backend that only speaks HTTP/1.x
- Raw socket clients writing an invalid request line

## Quick fix

1. URL-encode the path (spaces → `%20`)
2. Let the client negotiate the protocol instead of forcing it
3. Check proxy → backend protocol settings

## Detailed fix by platform

### Linux

1. Encode the URL:

```bash
curl "https://example.com/files/annual%20report.pdf"
```


## How to diagnose

1. **URL** — Any spaces or control characters?
2. **Protocol** — Which HTTP version does each hop use?

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Source: [WhatIsMyError](https://whatismyerror.com/errors/http/505-http-version-not-supported)