### Answer Here are some things to check when call transfers are repeatedly failing: 1. Verify Phone Number Format Ensure your transfer number is in E.164 format (e.g.,

+12137771234

) . [(1) ]() 2. Check the SIP Connection Log 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. [(2) ]() 3. Common Failure Causes - Telephony issues – Check the SIP status code in your call logs for specifics. - Human detection timeout – If you're using warm transfer with human detection enabled, the call may fail if a human isn't detected within the timeout period. - Carrier-level rejections – Random failures across different numbers can point to carrier-side issues like DND, invalid caller ID formatting, or permission errors (e.g.,

telephony_provider_permission_denied

) . [(3) ]() 4. Transfer Type If using warm transfer and experiencing issues, try switching to cold transfer to isolate the problem. [(1) ]() Next Steps: - Share your call ID(s) from the failed transfers so support can investigate the specific SIP error. - Review the [Debug call transfer failure]() guide for detailed troubleshooting steps. [(2) ]()

​ To learn more, see the sources I considered: [[1] Call Transfer Node](https://docs.retellai.com/build/conversation-flow/call-transfer-node) [[2] Debug call transfer failure](https://docs.retellai.com/reliability/call-performance) [[3] Warm Phone Transfer Node Failure](https://discord.com/channels/1186424376300679209/1442988791223554191) ​

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