Twilio to OpenAI SIP returns 408. Is project SIP gated per project?

API
1

I am integrating a phone voice agent with the Realtime API over SIP. Flow is simple. Twilio dials our number. Our TwiML returns sip:proj_[REDACTED]@sip.api.openai.com;transport=tls. OpenAI should emit realtime.call.incoming to our webhook so we can accept and run the session.

Our side is healthy. We verify and 200 correctly signed realtime.call.incoming tests with a call_id. We can access realtime models normally. TwiML is valid and returns the exact SIP URI.

Live calls fail. Twilio Call Insights shows the SIP leg to sip.api.openai.com ending with “Last SIP Response: 408 Request Timeout” and duration 0s. We receive no realtime.call.incoming webhook for these attempts.

Questions

  1. Does Realtime SIP routing require internal enablement per project?

  2. If yes, can OpenAI staff confirm and enable it for proj_[REDACTED]?

  3. Are there any extra requirements for the SIP INVITE beyond ;transport=tls that would cause a 408, such as specific headers or SDP constraints?

2

Did you figure out any way? in my case, it was working fine earlier (local system, ngrok) but then i hosted my application, and its not working/.