# Custom Sip Trunk - extension transfers on warm transfer **URL:** \ **Category:** Support Help\ **Created:** [January 13, 2026, 10:05am UTC](https://community.retellai.com/t/custom-sip-trunk-extension-transfers-on-warm-transfer/425 "2026-01-13T10:05:53Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Zac\_Pagan](https://yyz2.discourse-cdn.com/flex008/user_avatar/community.retellai.com/zac_pagan/32/390_2.png) [@Zac\_Pagan](https://community.retellai.com/u/Zac_Pagan)\ **Post date:** [January 13, 2026, 10:05am UTC](https://community.retellai.com/t/custom-sip-trunk-extension-transfers-on-warm-transfer/425/1 "2026-01-13T10:05:53Z")
I originally connected my phone number through sip trunking. When the agent takes the call and transfers via a dynamic warm transfer to an extension I have inputted, I hear the hold tone but I cant see any logs of a transfer actually made to my internal extension and the call logs just show no answer? ---
**Author:** ![support2](https://yyz2.discourse-cdn.com/flex008/user_avatar/community.retellai.com/support2/32/15_2.png) [@support2](https://community.retellai.com/u/support2)\ **Post date:** [January 13, 2026, 10:06am UTC](https://community.retellai.com/t/custom-sip-trunk-extension-transfers-on-warm-transfer/425/2 "2026-01-13T10:06:15Z")
Based on the available sources, when using warm transfer with extensions through SIP trunking, there are a few configuration points to verify: For the transfer target, you can set the transfer number to be a number in e.164 format, a SIP URI in the format of `sip:username@domain`, or a dynamic variable that gets substituted at runtime[(1)](https://docs.retellai.com/build/conversation-flow/call-transfer-node). When setting the transfer number extension, the extension must be 0-9, ‘\*’, ‘#’ (e.g., 123#)[(1)](https://docs.retellai.com/build/conversation-flow/call-transfer-node). If your transfer destination is not in e.164 format, you can choose to keep the input as is by choosing raw format when using custom telephony[(1)](https://docs.retellai.com/build/conversation-flow/call-transfer-node). This can be useful when you want to transfer to internal pseudo numbers[(1)](https://docs.retellai.com/build/conversation-flow/call-transfer-node). For warm transfers specifically, several settings affect the transfer behavior[(1)](https://docs.retellai.com/build/conversation-flow/call-transfer-node)[(2)](https://docs.retellai.com/build/single-multi-prompt/transfer-call): - **Enable human detection** : When enabled, the agent will check if a human is present after the transfer target answers[(1)](https://docs.retellai.com/build/conversation-flow/call-transfer-node)[(2)](https://docs.retellai.com/build/single-multi-prompt/transfer-call). The original caller will only be connected once a human is detected[(1)](https://docs.retellai.com/build/conversation-flow/call-transfer-node)[(2)](https://docs.retellai.com/build/single-multi-prompt/transfer-call). - **Agent detection timeout** : The maximum amount of time the AI agent will wait to determine whether the transfer target is a human[(1)](https://docs.retellai.com/build/conversation-flow/call-transfer-node)[(2)](https://docs.retellai.com/build/single-multi-prompt/transfer-call). The caller is connected only if human detection succeeds within this timeframe[(1)](https://docs.retellai.com/build/conversation-flow/call-transfer-node)[(2)](https://docs.retellai.com/build/single-multi-prompt/transfer-call). Otherwise, the transfer is marked as failed[(1)](https://docs.retellai.com/build/conversation-flow/call-transfer-node)[(2)](https://docs.retellai.com/build/single-multi-prompt/transfer-call). The default timeout is 30 seconds[(1)](https://docs.retellai.com/build/conversation-flow/call-transfer-node)[(2)](https://docs.retellai.com/build/single-multi-prompt/transfer-call). - **Navigate IVR** : Provide a prompt to help you navigate if the transfer target is an IVR system[(1)](https://docs.retellai.com/build/conversation-flow/call-transfer-node)[(2)](https://docs.retellai.com/build/single-multi-prompt/transfer-call). The “no answer” status in your call logs could indicate that the human detection timeout expired before detecting a human on the extension, or the extension itself didn’t answer within the configured timeout period. I recommend checking your warm transfer configuration settings, particularly the agent detection timeout and whether human detection is enabled, as these directly impact whether the transfer completes successfully. ---
**Author:** ![Omar\_Ashraf](https://yyz2.discourse-cdn.com/flex008/user_avatar/community.retellai.com/omar_ashraf/32/102_2.png) [@Omar\_Ashraf](https://community.retellai.com/u/Omar_Ashraf)\ **Post date:** [January 13, 2026, 3:43pm UTC](https://community.retellai.com/t/custom-sip-trunk-extension-transfers-on-warm-transfer/425/3 "2026-01-13T15:43:36Z")
Hello @Zac_Pagan Can you share a call id so I can check it? ---
**Author:** ![support2](https://yyz2.discourse-cdn.com/flex008/user_avatar/community.retellai.com/support2/32/15_2.png) [@support2](https://community.retellai.com/u/support2)\ **Post date:** [January 13, 2026, 3:43pm UTC](https://community.retellai.com/t/custom-sip-trunk-extension-transfers-on-warm-transfer/425/4 "2026-01-13T15:43:59Z")
I don’t have specific information about a user named @Zac_Pagan or their call ID in the available sources. If you’re looking to retrieve call information in Retell AI, you can use the Get Call API endpoint with a specific call ID[(1)](https://docs.retellai.com/api-references/get-call). The call ID format typically looks like `"119c3f8e47135a29e65947eeb34cf12d"`[(1)](https://docs.retellai.com/api-references/get-call) or `"Jabr9TXYYJHfvl6Syypi88rdAHYHmcq6"`[(2)](https://docs.retellai.com/api-references/register-phone-call). To retrieve call details, you would make a GET request to `/v2/get-call/{call_id}`[(1)](https://docs.retellai.com/api-references/get-call). If you need help with a specific call issue, please provide the call ID and I can help you understand what information you can retrieve about it. ---
**Author:** ![Zac\_Pagan](https://yyz2.discourse-cdn.com/flex008/user_avatar/community.retellai.com/zac_pagan/32/390_2.png) [@Zac\_Pagan](https://community.retellai.com/u/Zac_Pagan)\ **Post date:** [January 13, 2026, 11:00pm UTC](https://community.retellai.com/t/custom-sip-trunk-extension-transfers-on-warm-transfer/425/5 "2026-01-13T23:00:25Z")
Hi Omar, Caller ID: call\_be1ca415617633429aba6f39