### Answer You can transfer to a specific extension number by setting the transfer number extension field in your transfer call configuration [(1) ]() . The extension must be 0-9, '*', '#' (e.g., 123#) . For Custom SIP Headers: Yes, you can use custom SIP headers for call transfers [(2) ]() [(1) ]() . All header names must start with

X-

[(1) ]() . You can use dynamic variables for your custom SIP header values, allowing you to pass information extracted from the call to the receiving party [(2) ]() . Important Limitations: For cold transfers with transferee number using SIP REFER, different telephony providers may or may NOT honor the custom SIP headers in the REFER request . Twilio, for example, does not honor custom SIP headers in the REFER request, so the SIP headers you set in the transfer call tool will not work for cold transfer with transferee number when using Twilio . Setup Options: - **Conversation flow agents**: Check out the [call transfer node]() for configuration details - **Single/multi agent**: Check out the [call transfer function]() for configuration details If you're using custom telephony and your transfer destination is not in e.164 format, you can choose to keep the input as is by choosing raw format [(1) ]() .

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

​ To learn more, see the sources I considered: [[1] Transfer call](https://docs.retellai.com/build/single-multi-prompt/transfer-call) [[2] Set & parse custom SIP headers](https://docs.retellai.com/build/telephony/sip-headers) ​

### Answer Based on the available sources, the extension field is specifically mentioned in the Call Transfer Node documentation for Conversation Flow agents [(1) ]() . In the "Configure Transfer" section, after you set the transfer number, there's a step to "Set the transfer number extension if needed" . The extension must be 0-9, '*', '#' (e.g., 123#) . Where to find it depends on your agent type: - **For Conversation flow agents**: Look in the call transfer node configuration - **For Single/Multi-prompt agents**: Check the transfer call function configuration [(2) ]() If you're not seeing this field in your interface, it's possible that: 1. You may be looking in a different section than where the extension field appears 2. The field might be labeled differently in the UI than in the documentation 3. You may need to first configure the main transfer number before the extension field becomes visible Could you clarify which type of agent you're using (Conversation Flow or Single/Multi-prompt) ? This will help me provide more specific guidance on where to locate the extension field in your setup.

​ To learn more, see the sources I considered: [[1] Call Transfer Node](https://docs.retellai.com/build/conversation-flow/call-transfer-node) [[2] Set & parse custom SIP headers](https://docs.retellai.com/build/telephony/sip-headers) ​

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

### Answer Based on the community discussions, there appear to be ongoing issues with the extension field in the Call Transfer Node [(1) ]() . While the documentation mentions setting the transfer number extension (0-9, '*', '#') [(2) ]() , users have reported that the extension field doesn't appear in their interface or doesn't work as expected during real calls [(1) ]() . Alternative approach using Navigate IVR: For handling extensions with dynamic routing in Retell's Call Transfer Node, you should use the Navigate IVR feature instead [(3) ]() . When configuring a warm transfer in the Call Transfer Node: 1. Configure it as a warm transfer (not cold transfer) 2. Enable the Navigate IVR option 3. In the Navigate IVR prompt field, provide instructions like: "After connecting, press extension {{extension_number}}" 4. Use dynamic variables to pass the specific extension for each department This approach is more reliable than trying to append extensions directly to phone numbers, since the Navigate IVR feature is specifically built to handle IVR navigation and extension dialing . Important note about PBX limitations: Retell AI can only transfer calls to full PSTN numbers or SIP entry points, not directly to internal PBX extensions [(4) ]() . The recommended approach is to transfer the call back to the PBX via a dedicated DID or SIP trunk, then let the PBX route internally using IVR logic . A screenshot would be helpful to see exactly what option

s are available in your Call Transfer Node configuration.

​ To learn more, see the sources I considered: [[1] Call transfer extension number not working in call transfer node](https://discord.com/channels/1186424376300679209/1425942962810130452) [[2] Call Transfer Node](https://docs.retellai.com/build/conversation-flow/call-transfer-node) [[3] Using the dynamic transfer node in Retell's GUI with extensions](https://community.retellai.com/t/using-the-dynamic-transfer-node-in-retells-gui-with-extensions/195) [[4] Solved, call transfers are now routing my calls to extensions](https://community.retellai.com/t/solved-call-transfers-are-now-routing-my-calls-to-extensions/723) ​

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