### Answer --- To determine whether a transfer failed because nobody picked up vs. a configuration issue on your side: 1. Check the call logs for the SIP connection log and disconnection reason Call transfer failures occur for similar reasons as outbound call failures. The SIP connection log is available in the call logs and is useful for diagnosing the failure reason. [(1) ]() 2. Look at the

disconnection_reason

field When you retrieve the call via the API, the

disconnection_reason

field will indicate what happened. Relevant values include: [(2) ]() -

dial_no_answer

– The number dialed did not answer -

dial_busy

– The number dialed is busy -

user_declined

– The user explicitly declined the call 3. If using warm transfer with human detection enabled The transfer may fail if a human is not successfully detected. Possible reasons include: [(1) ]() - 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 4. Check the detailed logs In the logs, you'll see messages like: [(3) ]()

Error transferring call, SIP status code: undefined SIP error category: user_no_answer

This indicates the transfer destination did not pick up. **Summary**: If you see

dial_no_answer

or

user_no_answer

in your logs/disconnection reason, it means reception didn't pick up. If you see errors like

telephony_provider_permission_denied

,

sip_routing_error

, or

invalid_destination

, that points to a configuration issue on your side. [(2) ]()

​ To learn more, see the sources I considered: [[1] Debug call transfer failure](https://docs.retellai.com/reliability/call-performance) [[2] Debug outbound connection issues](https://docs.retellai.com/reliability/debug-outbound-call) [[3] Transfer](https://discord.com/channels/1186424376300679209/1397568596632146113) ​

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