### Answer Based on the sources, here are some troubleshooting steps for your advanced warm transfer failure: Common causes when warm transfer fails but normal transfer works: 1. Telephony/SIP issues - Call transfer failures often occur for similar reasons as outbound call failures. The SIP connection log in your call logs can help diagnose the failure reason. [(1) ]() 2. Human detection failure - If human detection is enabled, the call may fail if: - No human was actually present (e.g., it was an IVR or voicemail) - The other party spoke only after the detection timeout expired - The speech was too similar to an IVR or voicemail and wasn't recognized as human 3. Caller ID override not supported - If you're using the "User's Number" caller ID option and your telephony provider doesn't support caller ID override, the transfer will fail. Retell Twilio numbers support this on both warm and cold transfer, but Retell Telnyx numbers only support it via cold transfer (SIP REFER) . [(2) ]() [(3) ]() Suggested fixes: - Check your Agent detection timeout setting - the default is 30 seconds. If the transfer target takes longer to answer, the transfer will be marked as failed. - Try enabling Auto-greet - this makes the agent say "Hello" immediately when the transfer target picks up, which increases the likelihood of detecting a human. - Review the SIP connection logs in your call details for specific error messages. [(1) ]() Other users have reported similar advanced warm transfer errors - one case was escalated to the Retell team for investigation. [(4) ](

76300679209/1446288701801103382) If the issue persists, I'd recommend reaching out via [Contact Sales]() or checking [) for additional support.

​ To learn more, see the sources I considered: [[1] Debug call transfer failure](https://docs.retellai.com/reliability/call-performance) [[2] Call Transfer Node](https://docs.retellai.com/build/conversation-flow/call-transfer-node) [[3] Transfer call](https://docs.retellai.com/build/single-multi-prompt/transfer-call) [[4] Advanced Warm Transfer error](https://discord.com/channels/1186424376300679209/1446288701801103382) ​

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

### Answer Based on your payload, you're using an agentic warm transfer (chat with human before transfer) which involves a secondary agent (

transferAgent

) to handle the conversation with the transfer target. The sources I have don't contain detailed documentation specifically for the

agentic_warm_transfer

type or the

agenticTransferConfig

parameters you're using. The documented warm transfer settings cover standard warm transfers with features like: - On-hold music - Navigate IVR - Human detection with auto-greet - Agent detection timeout - Whisper message (private message to transfer target) - Three-way message (message to both parties) [(1) ]() [(2) ]() Your configuration references an

agentId

and

agentVersion

for a transfer agent, which appears to be a more advanced feature not fully detailed in the available sources. Suggestions: 1. Verify the

transferAgent

configuration - ensure the

agentId

(

agent_781fb6fda8b8f69ce31b1473f3

) and

agentVersion

(4) are correct and that agent is properly set up. 2. Confirm the transfer destination number is in E.164 format (which it appears to be:

+447949491457

) . [(3) ]() 3. Check if there are any SIP connection logs in your call details that might reveal the specific failure reason. Since this advanced agentic warm transfer feature isn't fully documented in my available sources, I'd recommend reaching out directly for support: - Visit [Contact Sales]() - Check [) Would you like me to try to provide a general answer about warm transfer configuration, or do you have additional details abo

ut the error?

​ To learn more, see the sources I considered: [[1] Transfer call](https://docs.retellai.com/build/single-multi-prompt/transfer-call) [[2] Call Transfer Node](https://docs.retellai.com/build/conversation-flow/call-transfer-node) [[3] Warm call transfer](https://discord.com/channels/1186424376300679209/1356928532101726338) ​

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

### Answer To raise this Advanced Warm Transfer issue with the Retell AI team, you have a few options: 1. Share your call ID in this Discord channel - Other users experiencing similar Advanced Warm Transfer errors were asked by Retell staff to share their call ID, which was then escalated to the team for investigation. [(1) ]() 2. Contact support via email - You can send a message to the support email. 3. Contact Sales - Visit [Contact Sales]() [(2) ]() 4. GitHub - Visit [) Based on the Discord thread, when you report the issue, include your call ID (e.g.,

call_72b28ff8b00ecd7f45f7b75a3e5

) as Retell staff will need this to investigate. [(1) ]() Note: Other users have reported similar Advanced Warm Transfer errors and these were escalated to the Retell team.

​ To learn more, see the sources I considered: [[1] Advanced Warm Transfer error](https://discord.com/channels/1186424376300679209/1446288701801103382) [[2] Here is how that can be fixed](https://retell.discourse.group/t/here-is-how-that-can-be-fixed/23) ​

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