### Answer This issue—where the call connects, you hear nothing, and it hangs up after you speak—can have a few causes with multi-prompt agents and Telnyx SIP trunking: ## Possible Causes & Troubleshooting Steps 1. Audio Echo / False User Detection A known issue is that the agent may detect an echo of its own voice as user speech, causing it to interrupt itself or behave unexpectedly. [(1) ]() One user reported that lowering interruption sensitivity to 0.65 resolved similar problems where the agent thought the user was speaking when they weren't. 2. SIP Trunking Configuration Since you're using Telnyx via SIP trunking, ensure your SIP trunk is properly configured in Retell. Audio issues and premature disconnects can occur if there's a mismatch in the SIP setup or if audio streams aren't correctly routed. [(2) ]() 3. Agent Prompt / First Message Setup Verify that your multi-prompt agent has a proper first message or "AI Initiates" configuration. If the agent has no initial greeting or the prompt is misconfigured, it may not speak at all. [(3) ]() 4. Check Call Logs Review the call logs and SIP connection logs in your Retell dashboard. The logs can reveal whether the issue is telephony-related (SIP errors) or agent-related (prompt/function issues) . [(4) ]() ## Recommended Actions - Lower the interruption sensitivity setting and test again - Confirm your Telnyx SIP trunk is correctly integrated with Retell - Check that your agent has a valid first message configured - Review the call logs for any error codes or disconnection reasons If the issue persists after these checks, I'd recommend reaching out via

[Contact Sales]() or checking the [Retell GitHub]() for additional support. Would you like a general answer on debugging SIP trunking issues, or do you have access to specific error messages from your call logs?

​ To learn more, see the sources I considered: [[1] multi-prompt agent cuts off welcome message](https://discord.com/channels/1186424376300679209/1394905893128110080) [[2] Platform Changelogs | Retell AI](https://www.retellai.com/changelog) [[3] Single/Multi Prompt Agent Overview](https://docs.retellai.com/build/single-multi-prompt/prompt-overview) [[4] Debug call transfer failure](https://docs.retellai.com/reliability/call-performance) ​

Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.

@AI Evy ?

### Answer Based on your description—call connects, no audio, then automatic hangup with

user_hangup

as the disconnection reason—this closely matches a known issue that was reported and resolved with Vonage SIP trunking, which may also apply to Telnyx. [(1) ]() ## What Likely Happened A similar issue was reported where calls ended immediately with

error_no_audio_received

and

user_hangup

. Investigation revealed that Retell's SIP endpoint was sending a BYE (ending the call) before media started, and no RTP packets were being sent. This was identified as a Retell-side issue, and a fix was rolled out. ## Recommended Steps 1. Verify Telnyx SIP Trunk Configuration Ensure your inbound settings use: -

+E.164

as the number format -

G722

,

G729

,

OPUS

as codecs -

TCP

as the transport method (UDP is temporarily not supported due to a connectivity issue) [(2) ]() 2. Check Outbound Authentication If you're making outbound calls, ensure the header

X-Telnyx-Username: <username>

is included when using credentials authentication. 3. Review Call Logs with Telnyx Ask Telnyx to confirm whether RTP packets are being received from Retell. If Telnyx shows the call established but no audio from Retell, this points to the same issue that was previously fixed. [(1) ]() 4. Contact Retell Support If the configuration is correct and the issue persists, this may require escalation. The previous similar issue was resolved after internal escalation. Would you like help verifying your Telnyx SIP trunk configuration?

​ To learn more, see the sources I considered: [[1] user_hangup Issue](https://discord.com/channels/1186424376300679209/1369254148637331507) [[2] Telnyx](https://docs.retellai.com/deploy/telnyx) ​

Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.