HTTP Status Codes
HTTP 426 Upgrade Required
426 Upgrade Required
The server refuses to perform the request using the current protocol and requires the client to upgrade.
Error AtlasError Documentation and ResolutionObserved message
426 Upgrade Required
Why it happens
- The request could not be fulfilled because of client-side syntax, state, authorization, or precondition issues.
- Headers, payload shape, request metadata, or client expectations do not match what the server requires.
- An application, proxy, or security layer rejected the request before normal processing could complete.
How to fix it
- Inspect the exact request URL, headers, body, and protocol details being sent.
- Review server expectations for authentication, validation, conditional headers, or resource state.
- Check proxies, API gateways, and middleware that might reject the request before it reaches the application.
Official reference
IANA: HTTP Status Code RegistryRelated errors
Explore more