Realtime API SIP inbound calls failing again before webhook dispatch

@OpenAI_Support @curt.kennedy

Hi OpenAI team,

We are seeing what appears to be a recurrence of a previous Realtime API SIP issue.

Related previous thread:

Invalid SDP error on new call to SIP endpoint API

The previously reported SIP SDP error is happening again. We are dead in the water trying to place new SIP calls into gpt-realtime. SIP/2.0 400 Bad Request Contact: sips:[my email]:5061 { “error”: { “message”: “Invalid SDP offer.”, “type”: “invalid_request_error”, “code”: “invalid_offer”, “param”: “” } }

Our current setup is:

Twilio SIP → OpenAI Realtime API SIP endpoint → OpenAI webhook → Google Cloud Run / sideband WebSocket

Current symptoms:

• New inbound SIP calls fail immediately.
• Twilio reports a SIP failure / 400 response.
• The OpenAI webhook is not triggered.
• We do not receive the usual realtime.call.incoming event.
• Our /accept flow is never reached.
• No sideband WebSocket connection attempt appears in our logs.
• We have not made any relevant changes to our code, Twilio configuration, SIP settings, or OpenAI configuration.

This looks very similar to the issue discussed in the thread above, where calls appeared to be rejected before webhook dispatch, possibly around SDP validation.

The issue started again around [2026-05-13 9:30 JST] / [2026-05-13 00:30 UTC] on our side.

Could someone from OpenAI please check whether there has been another regression or incident affecting Realtime API SIP ingress?

This is impacting our production voice service, so any confirmation or status update would be greatly appreciated.

Thank you.