### Answer The error "the other side declined the transfer" indicates the transfer destination is rejecting the incoming call. Here are troubleshooting steps: Check Your Transfer Configuration - Verify the transfer number is in e.164 format (e.g.,

+15551234567

) or a valid SIP URI in the format

sip:username@domain

[(1) ]() - Confirm the transfer number extension is correct if used—extensions must be 0-9,

*

,

#

(e.g.,

123#

) Telephony-Related Causes Call transfer failures occur for similar reasons as outbound call failures. Check the SIP connection log in your call logs for specific error codes that can help identify the exact issue. [(2) ]() Recommended Actions 1. Review your call detailed logs for specific SIP error codes [(3) ]() 2. Test transferring to a different number to determine if it's number-specific 3. If using custom telephony, check with your provider's logs and support team 4. Ensure the transfer destination number is active and able to receive calls If you're using warm transfer with human detection enabled, the call may also fail if a human is not successfully detected at the destination (e.g., it reached voicemail or IVR instead) . [(2) ]() For further investigation, I'd recommend creating a ticket in #❓・bug-report with your call IDs so the Retell team can examine the specific SIP logs. [(4) ]()

​ To learn more, see the sources I considered: [[1] Transfer call](https://docs.retellai.com/build/single-multi-prompt/transfer-call) [[2] Debug call transfer failure](https://docs.retellai.com/reliability/call-performance) [[3] tool_call_id: transfer_call_f246b8{"status":"Transfer call cannot be completed, telephony provider](https://discord.com/channels/1186424376300679209/1393151424631668780) [[4] Discord message from @mauvatar on 2026-01-19](https://discord.com/channels/1186424376300679209/1294891368505937952/1462849273413632221) ​

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

Appreciate the feedback! Feel free to ask me again with additional guidance or context.