### Answer --- When a call transfer goes silent, there are a few things to check: 1. Verify Call Type Call transfer only works during phone calls, not web calls. [(1) ]() 2. Check Transfer Destination Format Ensure your transfer number is either: [(2) ]() - A number in e.164 format (e.g.,

+14155551234

) - A SIP URI in the format

sip:username@domain

- A dynamic variable that gets substituted at runtime 3. Telephony Issues Call transfer failures often occur for similar reasons as outbound call failures. The SIP connection log is available in your call logs and is useful for diagnosing the failure reason. [(1) ]() 4. If Using Warm Transfer with Human Detection If human detection is enabled, the call may fail if a human is not successfully detected. Possible reasons include: - No human was actually present (e.g., it was an IVR or voicemail) - The other party spoke, but only after the detection timeout expired - The speech was too similar to an IVR or voicemail and was not recognized as human 5. Caller ID Override Issues If you have "User's Number" selected for caller ID and your telephony provider doesn't support caller ID override, the transfer would fail. [(2) ]() Could you share more details about your setup—are you using warm or cold transfer, and what telephony provider are you using?

​ To learn more, see the sources I considered: [[1] Debug call transfer failure](https://docs.retellai.com/reliability/call-performance) [[2] Transfer call](https://docs.retellai.com/build/single-multi-prompt/transfer-call) ​

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