What does HRESULT 0x80EF01F9 (RTC_E_STATUS_SERVER_VERSION_NOT_SUPPORTED) mean?

RTC_E_STATUS_SERVER_VERSION_NOT_SUPPORTED

Operational meaning: RTC_E_STATUS_SERVER_VERSION_NOT_SUPPORTED

In the RTC Client API, this result separates one failure or completion path from its neighbors because it denotes the server does not support the SIP protocol version in the request.

At the HRESULT layer, this result appears as 0x80EF01F9 in the RTC SIP-status facility carrying status 505; preserving the facility and symbol prevents it from being grouped incorrectly with unrelated networking or media errors.

A defensible diagnosis of this result requires you to capture the exact request line, serializer version token, and any intermediary that rewrote it; in the case, Version Not Supported concerns SIP-Version, not an unsupported extension option or media version.

Signals worth preserving

• Code-specific proof: capture the exact request line, serializer version token, and any intermediary that rewrote it.
• Correlation key: status-specific headers.
• Protocol or object snapshot: retry or alternate-target decision.
• Last completed transition: request method and Request-URI.
• Expected output: responding Via hop.

Recovery and control flow

The owning RTC component should use a protocol version supported by both sides and fix any component emitting a malformed version token; it should also settle or cancel its previous operation before callers begin a replacement.

Example: A custom transport sends an invalid SIP version in the request line to a compliant server.

Protocol and object state

The facility code preserves the SIP status number; diagnosis should start with the method and responding hop rather than treating every value as a local COM failure. Some responses invite a modified request or authenticated retry, while others are terminal for the current target or even global for the addressed user.

Verification workflow

1. Collect enough evidence to capture the exact request line, serializer version token, and any intermediary that rewrote it.
2. Test the competing explanation explicitly, because Version Not Supported concerns SIP-Version, not an unsupported extension option or media version.
3. Apply the targeted fix — use a protocol version supported by both sides and fix any component emitting a malformed version token — and validate both protocol completion and object cleanup.

Actions that do not address this condition

• Do not show a reason phrase as trusted server identity or authorization evidence.
• Do not retry every 4xx or 5xx response with the identical request.

Do not confuse it with

Comparison point: 420 Is for mandatory extensions, while 505 is for the base protocol version.

Technical references

• Microsoft RTC return constants.
• SIP response semantics.