Overview

A 505 HTTP Status Code (officially called "505 HTTP Version Not Supported") is a server-side error. It means the web server received an HTTP request from your browser, but it refuses—or doesn't know how—to process it using the specific HTTP protocol version that was sent in the request.

What Causes a 505 Error?

Because it is a 500 series error, the root issue typically resides on the server side, though it can be triggered by how the request was sent or modified along the path:

• Outdated Web Server Software: The origin web server software is running an older build that does not support modern protocol versions (like HTTP/2 or HTTP/3).

• Corrupted Request Headers: A web browser extension, VPN, or network proxy modified or corrupted the HTTP request headers sent to the server.

• Aggressive Firewalls / Security Rules: A firewall, Web Application Firewall (WAF), or CDN (such as Cloudflare) between the user and the origin server is misconfigured or actively rejecting the requested protocol version.

Troubleshooting & Self-Service Steps

1. If You Are a Website Visitor

Try these quick client-side checks to rule out local browser or network issues:

• Test in Incognito / Private Mode: A corrupted cookie or browser extension may be altering your HTTP headers. Testing in an Incognito/Private window isolates extension-based conflicts.

• Update Your Web Browser: Ensure your browser is updated to the latest version so it communicates using current, standard HTTP specifications.

• Clear Browser Cache and Cookies: Outdated session data stored in your browser can occasionally cause protocol negotiation mismatches.

• Disable VPNs or Local Proxies: If you are using a VPN, custom proxy, or third-party security suite, temporarily turn it off—some security software modifies network traffic headers in ways web servers reject.

2. If You Are a Website Owner or Server Admin

If you manage the web hosting account or server:

• Check Server Logs: Inspect your web server access and error logs (e.g., Apache or Nginx error logs in Plesk or cPanel) to review the exact raw HTTP request and user-agent that triggered the 505 response.

• Update Web Server Software: Ensure your web server software (Apache, Nginx, LiteSpeed, etc.) is updated to a supported release that properly negotiates modern protocols (HTTP/1.1, HTTP/2, and HTTP/3).

• Check CDN & Reverse Proxy Settings: If you use a proxy like Cloudflare or Nginx in front of Apache, verify that protocol settings match between the edge proxy and the origin server.

Need Extra Help?

If basic self-service troubleshooting does not resolve the error, or if you require technical support to inspect server-level protocol configurations:

• Action: Connect directly with a Live Agent via chat, phone call or email.