Inbound phone calls connect (SIP OK) but NO AUDIO — RTP not flowing through LiveKit SBC

Support Help
1

Setup: Twilio Elastic SIP Trunk → sip.retellai.com, two +57 (Colombia) numbers.

Problem (started 24-Jul, worked fine 23-Jul, no changes on our side): inbound phone calls
connect at the SIP layer and the agent’s greeting TTS is generated, but there is NO audio in
either direction and ZERO ASR events (user turns = 0). The caller hears nothing and hangs up
after a few seconds; the call is logged as user_hangup.

Why this looks like a LiveKit SBC / RTP issue, not our setup:

  • Web/WebRTC test calls work perfectly today (132s, 22 bidirectional turns) → agent, LLM,
    TTS and our backend are all fine.
  • Both +57 numbers fail identically (same trunk) → account/platform level.
  • Twilio shows all calls completed, no errors, healthy balance → their side is fine.
  • Matches known threads: “one-way audio”, “RTP not flowing outbound from LiveKit”,
    “calls dropped at the LiveKit level (logged as user hangup)”.

Muted call IDs (today, 24-Jul):

  • call_5c50a071ea095a3b374f8c60e81
  • call_6e2903ac52fc822b5ed72448a3c
  • call_3cb7f8ae29ac9964e5b6d15d0c6
    Working call WITH audio (23-Jul): call_fcca1eb5f9efd6cd9ddb1e6679b

Questions:

  1. Is this the known one-way-audio / RTP-not-flowing-from-LiveKit regression?
  2. Is the LiveKit region serving our +57 numbers degraded? Can we be routed to another region?
  3. Workaround or ETA? This is production-blocking for a live business.

Agents: agent_2ea44a0ac6bbc83558e689107b, agent_0b95eea5ea977faa367294adea
Account: brainaia25@gmail.com

2

Hello @brainaia25 I have reported this to the team for further investigation. We’ll get back to you as soon as we have an update.

Thank You

4

Hi @Shah-Fazal, thank you — I really appreciate how fast you escalated this.

Good news: as of ~12:10 COT today (25-Jul), the audio is back — our inbound phone
calls (Twilio Elastic SIP Trunk → sip.retellai.com) have two-way audio again.

Before I rely on this for live clients, could you help me confirm a few things:

  1. Did the team apply a fix on your side, or did it recover on its own?
  2. Is it stable now, or is there a risk it could regress?
  3. Do you know the root cause — was it the LiveKit RTP / SBC issue, and was it
    regional for our +57 (Colombia) numbers?

Knowing whether this was a permanent fix vs a transient recovery matters a lot to me,
as I’m about to onboard paying clients on this line. Thanks again for the quick help!

5

Hey @brainaia25 Your issue has been passed on to our engineering team for further investigation. At the moment, I don’t have any confirmation or update from them yet. I’ll let you know as soon as I receive any news.

Thank You

6

Hey @brainaia25 We checked the examples you sent and it seems we are not receiving media from Twilio side. we would suggest opening a ticket with Twilio support to debug the audio issue.

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Thank You