Can't transfer calls out Vapi AI #support

Can't transfer calls out

Ziggy

04/05/2025, 9:39 PM

1ce7482d-a6a6-49da-9e02-5db14d6d294b Above is an example of a call ID. I have created a transfer_call_tool yet it doesn't seem able to transfer the call out for me, it just hangs up when it tries. I've included the number in the call forwarding section of the assistant, and given it the tool, and told it to call the tool when transferring.

Vapi Support Bot

04/05/2025, 9:40 PM

Hi there! I see you're having trouble with the

transfer_call_tool

- calls are hanging up instead of transferring properly. I'm unable to access the specific logs for your call ID, but I can definitely help troubleshoot this issue based on common problems with Vapi call transfers. Based on the information I found, here are some potential causes and troubleshooting steps: ### Common Issues That Might Be Causing This 1. **SIP REFER Handling Issues**: Vapi uses SIP REFER for call transfers, which might not be handled correctly by your receiving system. According to [multiple user reports](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1337383511329345588), this is a common cause of calls hanging up during transfer. 2. **Configuration Issues**: There might be a misconfiguration in your assistant's settings. Make sure the

forwardingPhoneNumber

is in the correct E.164 format (e.g., +15558675309) as [mentioned in troubleshooting guides](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1335869152535121960). 3. **Server Event Interference**: If you have enabled the server event

'phone-call-control'

, this could be causing the issue. This event allows you to handle call transfers instead of Vapi, which might lead to conflicts as [noted in support documentation](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1330092161835733013). ### Troubleshooting Steps 1. **Check Your Logs**: Navigate to the Vapi Dashboard > logs > calls to review any error messages associated with your call ID (1ce7482d-a6a6-49da-9e02-5db14d6d294b). 2. **Verify Phone Number Format**: Ensure your destination number is in E.164 format and is valid. Also note that [Vapi numbers can only call US and Canada numbers](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1336713212233515089).

Vapi Support Bot

04/05/2025, 9:41 PM

3. **Check Assistant Overrides**: If you're using the

transferCall

tool, ensure that you're setting the

assistantOverrides

correctly to prevent unwanted messages during transfer as [recommended by Vapi support](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1336569634094186516). 4. **Try Alternative Transfer Methods**: Consider whether Vapi can use SIP INVITE instead of REFER (

"sipVerb": "invite"

Vapi Support Bot

04/05/2025, 9:41 PM

- [Discord Thread on Contacting Support](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1333747605628391434)

Vapi Support Bot

04/05/2025, 9:41 PM

Hi there! I'd be happy to provide more details on troubleshooting your call transfer issue. I'm unable to access the specific logs for your call ID, but I can definitely provide more information on the troubleshooting steps mentioned earlier. Let me elaborate on some of the most common solutions that have helped other users with similar issues: ### More Details on Assistant Overrides When using the

transferCall

tool, make sure your

assistantOverrides

are correctly configured. Some users have reported that the system speaks a transfer message despite attempts to disable it. According to [troubleshooting documentation](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1336569634094186516), properly setting these overrides can prevent unwanted messages during the transfer process. ### Check for "No Transfer Destination Returned" Error One common issue is that the

transferCall

tool might be called, but the result shows "No transfer destination returned." This suggests a potential issue with how the transfer destination is configured or passed to the tool as [noted in user reports](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1336644455582928906). ### Verify Destination Number Limitations Ensure your destination number is valid and reachable. Remember that Vapi numbers can only call US and Canada numbers as [mentioned in the documentation](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1336713212233515089). If you're trying to transfer to an international number, this could be causing the issue. ### Check for Server Event Conflicts If you have the server event 'phone-call-control' enabled, try removing it from your assistant. This event allows you to handle call transfers instead of Vapi, which might be causing conflicts as [reported by other users](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1330092161835733013).

Vapi Support Bot

04/05/2025, 9:41 PM

### SIP System Compatibility There could be compatibility issues between the VAPI transfer method and your SIP system. According to [troubleshooting guides](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1334919245468799007), network issues, firewall settings (like SIP ALG), or specific SIP system requirements might be affecting the transfer. ### Using Your Call ID for Support The call ID you provided (1ce7482d-a6a6-49da-9e02-5db14d6d294b) is very useful for debugging. When contacting Vapi support, provide this ID along with details about when the issue occurred and what you expected to happen. This helps them track down the specific problem in their logs as [recommended in support documentation](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1334044698364350474). Would you like me to explain any of these points in more detail, or is there a specific aspect of the call transfer process you'd like to focus on? Sources: - [Discord Thread on Assistant Overrides](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1336569634094186516) - [Discord Thread on No Transfer Destination](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1336644455582928906) - [Discord Thread on Vapi Number Limitations](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1336713212233515089) - [Discord Thread on Server Event Interference](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1330092161835733013) - [Discord Thread on SIP System Compatibility](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1334919245468799007) - [Discord Thread on Using Call ID for Support](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1334044698364350474)

Kyle Brunker

04/06/2025, 8:42 AM

Hey Ziggy, you need to check inside your Twilio call logs why the call was not forwarded. From our side, the call forwarding was successful, and it's visible inside the ended region as well. Check your Twilio logs and let me know if possible share them as well.

Previous Next