I have sent an email to support but have had no response so I am asking the Discord community for help. I'm experiencing a persistent one-way audio issue on inbound phone calls through a Telnyx number. Shirley (my VAPI assistant) speaks normally and callers can hear her, but VAPI never receives or transcribes the caller's voice. Every call ends with a 30-second silence timeout. Account / Org ID: 9bac25b0-6e91-47c9-bc33-c7ec779ad58b Phone number: +31 345 238 007 (Telnyx) Reference call ID: 019e1c53-35bc-7ddb-a672-6ac91ce54f36 (2026-05-12, 15:14:35 UTC) What the VAPI log shows for the reference call: Deepgram connects successfully with channels: 2, language nl, model nova-2 All Deepgram transcripts are channel: assistant (Shirley's own speech) Zero channel: user transcripts throughout the entire call Call ends: silence-timed-out after 30 seconds, endedReason: silence-timed-out What the Telnyx CDR shows: Call connected successfully, NORMAL_CLEARING, answered within 1 second Codec: PCMA (G.711 A-law) MoS: 4.4898, Quality: 98.75% Hangup initiated by VAPI (send_bye) What I have ruled out: Tested with two different callers on two different phones — same result Phones confirmed not muted Transcriber settings: Deepgram Nova 2, Dutch, confidence threshold 0.40, Smart Endpointing set to VAPI Telnyx number is imported into VAPI and correctly assigned to the assistant The caller's audio appears to reach Telnyx successfully but is not being passed through to VAPI's media/transcription pipeline. Could you check whether there is a SIP media routing issue on your end for inbound Telnyx calls using PCMA codec for this account? Attached call logs https://cdn.discordapp.com/attachments/1505869476933931138/1505869477097635901/calls-export-9bac25b0-6e91-47c9-bc33-c7ec779ad58b-2026-05-18-09-44-14.csv?ex=6a0c31bd&is=6a0ae03d&hm=5ee0eee967aa98370489d57bae3056062c61315dac239b0b283b5a7091667a3e&

Hey, looked at your call logs both calls show the same pattern: 41s duration, silence-timed-out, zero user transcripts. This is consistent across calls so it's a reliable bug, not a fluke. Most likely cause: PCMA codec mismatch. Telnyx is sending G.711 A-law but VAPI's media pipeline likely expects PCMU or Opus the caller audio arrives but gets dropped before Deepgram sees it. I've seen this exact issue before. It's a PCMA codec mismatch Telnyx is sending G.711 A-law but VAPI's media pipeline drops it before Deepgram ever sees the audio. Your Telnyx CDR looking perfect confirms the break is happening on the VAPI SIP ingestion side. I can help you get this sorted feel free to connect with me @Mike P

Hi Mike, Thanks for your patience, we've looked into this and have a workaround we'd like you to try. Rather than using the standard Telnyx number import, we recommend connecting your Telnyx number to Vapi via SIP Trunking instead. This gives Vapi direct control over the media path and should resolve the one-way audio issue you're seeing. Here's the guide to set it up: https://docs.vapi.ai/advanced/sip/sip-trunk The steps at a high level: 1. Set up a SIP trunk in your Telnyx account pointing to Vapi's SIP URI 2. Add it as a SIP trunk in Vapi 3. Assign your assistant to it Could you give this a try and let us know if it resolves the issue? Happy to help you through any step of the setup. Best, Chiranjeet Vapi Support

Hi Chiranjeet 👏 Thank you for the info. The problem has been resolved using the SIP Trunking. Appreciate the support Mike