HTTP 505 HTTP Version Not Supported
The server doesn’t support the HTTP protocol version used in the request.
Exact message you may see
HTTP Version Not Supported
Seen on:
Linux
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
- URL-encode the path (spaces →
%20) - Let the client negotiate the protocol instead of forcing it
- Check proxy → backend protocol settings
Detailed fix by platform
Linux
- Encode the URL:bash
curl "https://example.com/files/annual%20report.pdf"
How to diagnose
- URL — Any spaces or control characters?
- Protocol — Which HTTP version does each hop use?
🔧 Still not fixed?
Many errors look alike. If the steps above didn’t solve it, one of these is probably what you’re facing:
Most viewed in HTTP
Other ways to find it
Where this error sits
Origin: Network. Errors that are often confused with or caused by this one (click to open):
🧠 Still stuck? Analyze your error
Paste the full message, response headers or stack trace — we'll detect the platform and point to the most likely cause.
💬 What worked for others
No tips yet — did something else fix this for you?
Share what worked for you
Tips are checked by an editor before they appear. Links are removed.
Did this fix work for you?
Report a correction or suggest an improvement
Last updated 11 Oct 2026