Hey Vapi team, I’m having a Telnyx inbound audio issue. Summary: - Web/WebRTC calls to the same assistant work perfectly. - BUT inbound calls through my imported Telnyx number have extremely broken/choppy caller audio (I can hear tiny fragments of my voice, but it’s unusable and does not get transcribed). Feels like a codec / packetization / media negotiation problem (not total no-audio). Vapi details: - Call ID: 019d0630-a659-755c-ad8e-e1ce9d67eda7 - Assistant ID: b371d9ee-4d08-4c06-afb1-e14ce5c2c2af - Phone Number ID (Telnyx): 4d4cdc7f-f7ee-4fc6-8da2-5d778d27a572 - Telnyx transport IDs from the call: - callLegId: dfb22f80-2393-11f1-9403-02420a1f0b70 - callSessionId: dfb221c0-2393-11f1-957d-02420a1f0b70 - callControlId: v3:-pV5LCbohVFweX8fekC_PozZ9KBbOep1Fk35GtLYzSVEkX0Ficl85A What I tried: - Forced Telnyx codec settings (G.711 / “codec only”) but it didn’t fix it. - Vapi side is basically the default Telnyx integration config (auto-set). Question: Can someone help me diagnose what is happening on this call and what I should change in Telnyx (or Vapi Telnyx settings) to get clean audio? Happy to run another test call if you tell me what to change / what logs to collect.

Thanks for the detailed info! To help diagnose the choppy audio, could you please confirm if you have a SIP packet capture (PCAP) or call logs from Telnyx for the affected call? If so, sharing a snippet or summary of the media negotiation/codec section would be very helpful for pinpointing the issue. If you need instructions on how to obtain a PCAP or which logs to collect, let me know! Sources: - [Telnyx SIP integration documentation](https://docs.vapi.ai/advanced/sip/telnyx) - [Debug call forwarding drops & SIP troubleshooting](https://docs.vapi.ai/phone-calling/in-call-control/transfer-calls/debug-forwarding-drops)

sure, here it is https://cdn.discordapp.com/attachments/1484190907787120740/1484205105938169877/LU-1773927277251339-124646930bcf.isbc401.nokia.com.pcap?ex=69bd6138&is=69bc0fb8&hm=6a05282cc435c312a4aec8630656cce27640cb033be83af55834a51d1022a127&

This feels more like an RTP/media issue than just codec, especially since WebRTC is clean but SIP audio is breaking up. I’d look at Telnyx RTP settings (ptime, jitter buffer, NAT/symmetric RTP) and make sure Vapi is actually getting a stable stream. Also double-check it’s sending PCMU (G.711 μ-law) consistently at ~20ms packets. Happy to go through this with you and review the logs together, are you running this behind NAT or using something like Asterisk/SBC in between? @Onurson

Hey Ramsey, thanks so much. To clarify: I’m using a Telnyx Voice API Application connected directly to Vapi. It’s a straight cloud-to-cloud setup with no Asterisk, SBC, or local NAT involved. I checked the logs and the call is actually negotiating PCMA (G.711 A-law) with payload type 8, rather than PCMU. Since this is a German number, that’s the default. Do you think this codec difference is causing the issues, or should I force Telnyx to use PCMU? I am not sure how to look up the RTP settings, but they are all just standards and thus should be configured correctly by Telnyx. What steps should I take next? Are we sure this is not a Vapi-related thing? Because it worked before, I changed nothing on Telnyx, just some settings in Vapi, and now it does not work anymore. My gut feeling tells me it's not a Telnyx thing. I am going to try some stuff. If you have any next steps or ideas in the meantime, let me know. @Ramsey EDIT: I found out that this happens only some of the time. In phases. For 10 calls the quality was good. Then it suddenly stopped working again

Hi, I looked into both issues you’re facing and here’s a clear breakdown along with the next steps. ---- Issue 1: Choppy / Broken Audio on Inbound Calls This is likely due to a codec mismatch. If you need a quick workaround, using a US-based Telnyx number should resolve this, as those typically negotiate PCMU, which our system handles reliably. ---- Issue 2: Telnyx Number Import (400 Error) This error is coming directly from Telnyx when we attempt to associate the phone number with your Vapi application during the import process. Since you were able to import a different number successfully, your API key and setup are working correctly this issue is specific to the affected number. Common reasons: • The number is not fully active yet (still provisioning or porting) • The number belongs to a different Telnyx account/sub-account • The number has restrictions (e.g., messaging-only or not eligible for call control) ---- Recommended Steps 1. Log into your Telnyx portal: https://portal.telnyx.com 2. Go to Numbers and locate the affected number 3. Ensure the status is Active (not pending/porting) 4. Confirm it belongs to the same account as your API key 5. If everything looks correct: • Delete your Telnyx credential in Vapi (Settings → Keys) • Re-add it using your API key • Retry importing the number (I do see you tried it, lemme know still you are facing this) If the number has voice restrictions, you may need to use a voice-enabled number instead. ---- These steps should help resolve both the audio issue and the import error. Please let us know how it goes or if you’d like us to take a closer look.