505 HTTP Version Not Supported — Causes & Fix
HTTP 505 (HTTP Version Not Supported) means the server doesn't support the HTTP protocol version used in the request.
- Applies to
- Any website or web server (HTTP standard)
- Time to fix
- 15 minutes – 2 hours
What it means
Causes include a client using an HTTP version the server rejects, or a misconfigured server. This is a server-side (5xx) error defined in RFC 9110 (HTTP Semantics) — the request was valid, so the fix is on the server/origin side, not the visitor's.
Symptoms
- "505 HTTP Version Not Supported"
- A specific client fails to connect
How to fix it
- 1
Use a supported HTTP version
1. Configure the client to use an HTTP version the server accepts.
- 2
Fix server config (operator)
1. Ensure the server supports the expected HTTP versions.
Frequently asked questions
What triggers 505?
A mismatch in HTTP protocol version between client and server. Update the client or server so both speak a supported version.
Last updated July 20, 2026
Guidance only — always consult a qualified professional or the official service manual before carrying out repairs.