- Software and digital services
- HTTP service
505
HTTP 505 HTTP Version Not Supported: the request used an unsupported major HTTP version
Risk level
Low
Usually safe to check without specialist tools.
Urgency
Medium
Quick answer
HTTP 505 means the server does not support or refuses to support the major HTTP version used in the request message.
Safety first
Stop and check this first
- Do not disable TLS verification or downgrade to an obsolete insecure protocol as a shortcut. Use a version the service explicitly supports.
Safe checks you can perform
- Record the negotiated and requested versions
- Test a documented supported version
- Identify the version-rejecting hop
Leave these tasks to a qualified professional
- Do not attempt this professional task: Repair protocol negotiation across the chain
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Repair protocol negotiation across the chain
What they doAlign TLS ALPN, proxy protocol settings and origin support while keeping secure supported versions enabled.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Record the negotiated and requested versions
Capture safe connection metadata such as ALPN result and HTTP major version without collecting session keys or private payloads.
Do not disable TLS verification or downgrade to an obsolete insecure protocol as a shortcut. Use a version the service explicitly supports.
Evidence: RFC 9110 section 15.6.6 - 505 HTTP Version Not Supported · IANA Hypertext Transfer Protocol Status Code Registry
Test a documented supported version
Use a standard client configured for a protocol the response or service documentation explicitly supports.
Do not disable TLS verification or downgrade to an obsolete insecure protocol as a shortcut. Use a version the service explicitly supports.
Evidence: RFC 9110 section 15.6.6 - 505 HTTP Version Not Supported · IANA Hypertext Transfer Protocol Status Code Registry
Identify the version-rejecting hop
Compare edge, proxy and origin telemetry to locate where the request version changed or was refused.
Do not disable TLS verification or downgrade to an obsolete insecure protocol as a shortcut. Use a version the service explicitly supports.
Evidence: RFC 9110 section 15.6.6 - 505 HTTP Version Not Supported · IANA Hypertext Transfer Protocol Status Code Registry
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Software and digital services
- Brand
- HTTP
- Product type
- HTTP service
Known code variants
- 505 HTTP Version Not Supported
- 505 HTTP-Version nicht unterstützt
- 505 Versión HTTP no compatible
- 505 Version HTTP non prise en charge
- 505 Versione HTTP non supportata
- código HTTP 505
- error HTTP 505
- HTTP 505
- HTTP error 505
- HTTP status 505
- status code 505
What it means
The server cannot or will not complete the request with the same major version. Its response should explain why and identify other protocols it supports.
Warnings and stop conditions
- Higheditorial warning
Do not disable TLS verification or downgrade to an obsolete insecure protocol as a shortcut. Use a version the service explicitly supports.
Evidence: RFC 9110 section 15.6.6 - 505 HTTP Version Not Supported · IANA Hypertext Transfer Protocol Status Code Registry
Symptoms and causes
Probable causes · in order
- The client sent an unsupported major versionConfirmed
A legacy, experimental or malformed request can use a version the receiving server is unwilling to process.
Evidence: RFC 9110 section 15.6.6 - 505 HTTP Version Not Supported · IANA Hypertext Transfer Protocol Status Code Registry
- A proxy translated or rejected the protocol incorrectlyPossible
Version negotiation can fail at an intermediary even when the client and origin each support another compatible path.
Evidence: RFC 9110 section 15.6.6 - 505 HTTP Version Not Supported · IANA Hypertext Transfer Protocol Status Code Registry
Virtual technician
Does 505 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
RFC 9110 section 15.6.6 - 505 HTTP Version Not Supported
Internet Engineering Task Force · 2022 · official_doc
- 2
IANA Hypertext Transfer Protocol Status Code Registry
Internet Assigned Numbers Authority · 2025 · official_doc
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