Hey Everyone! We tried to build a "router" agent what could routre the conversation based on the user's lanugage (For the wide multilinugality needs.), but we couldn't. The Workflow was not good fit for this. Squad neither, the squad doesn't worked good for us, but doesn't really matter. But the transfer call. We believe the transfer funcition (as a tool), would be the best option for this solution, but sadly it didn't worked. It showed an error message and just failed. Now currently we moved foward from this point and find a solution (Make automation, recieve webhook, trigger Vapi module to "launch" outband call.), but this solution is not to scalable and not to professional. Basically we couldn't use it. So please help me with that what are the experiences or what could be the solution? If needed I can build fastly a "demo" where I can show the issue. Thanks Kevin

A common cause of transfer call failure is missing the required

destination

parameter in your

transferCall

tool configuration. Try updating your tool's parameters as shown below:

json
"parameters": {
  "type": "object",
  "properties": {
    "destination": {
      "type": "string",
      "enum": ["+1234567890"], // Replace with your external number in E.164 format
      "description": "The destination to transfer the call to."
    }
  },
  "required": ["destination"]
}

Make sure your telephony provider supports SIP REFER, as Vapi uses this for call transfers. [More details here](https://docs.vapi.ai/call-forwarding#2-using-the-transfercall-function). Source: - [Vapi documentation: call forwarding](https://docs.vapi.ai/call-forwarding)

Hi Calvin, If you're experiencing issues with call transfers dropping right after initiation, here's a concise troubleshooting guide: 1. Check the Call Ended Reason - Use the API to retrieve the ended reason of the call using:

shell
     curl -X GET "https://api.vapi.ai/call/{call_id}" \
     -H "Authorization: Bearer YOUR_API_KEY" \
     -H "Content-Type: application/json"

- If

endedReason

is not

assistant-forwarded-call

, review your assistant's configuration. [Debug call forwarding drops](https://docs.vapi.ai/phone-calling/transfer-calls/debug-forwarding-drops) 2. Server Message Configuration - Ensure

"phone-call-control"

is not in

serverMessages

unless implementing custom logic. 3. Phone Call Provider Bypass - Set

phoneCallProviderBypassEnabled

to

false

for Vapi-managed transfers. 4. Transfer Scenario Compatibility - Ensure your transfer scenario is supported. For example, web-to-phone transfers are not permitted. 5. Telephony Provider Logs - Check the logs in your telephony provider’s dashboard using the

phoneCallProviderId

extracted from the Vapi call object for any issues. 6. SIP Packet Analysis (if applicable) - Analyze SIP packets to check for

REFER

packets and provider responses using Wireshark. Make sure the destination number formats are correct and that the numbers are reachable, including factor aspects like call blocking. For setting up or managing call forwarding via Vapi, consider reviewing the [Call Forwarding guide](https://docs.vapi.ai/call-forwarding) for detailed configuration steps and examples.

Hi Aniah, Thank you for the answer! I tried out the 1. point, in the attached picture you can find the result. 2. point: Yes I called it from a phone number and I tried to trasnfer it to another one. 3. point: I don't get that. Not sure what is the task for me by that suggestion and where should I search for. 4. point: Yes, it's supported. 5. point: What should I search in that Log? 6. point: No it's not applicable sadly. By the way, I use Vonage for the phone numbers. There I can find fowarding settings (I attached 2 picture about.), but Im not sure what should I do. Cause I don't have "SIP URI" number. And about the phone number, now there Im not sure which webhook should goes there. So please help me a bit deeper in this issue, cause I really feel lost in it, and I would need this function in our projects. Thank you! https://cdn.discordapp.com/attachments/1417390884663726220/1418143695437434963/Transfer_call_issue_1.png?ex=68cd0cbc&is=68cbbb3c&hm=2ab20127a97b1b658efd9563d1165536b16c55a4b6065e788644ffd947f93bbd& https://cdn.discordapp.com/attachments/1417390884663726220/1418143695718322186/Vonage_Number_fowarding.png?ex=68cd0cbc&is=68cbbb3c&hm=a5bd053f73db3bbc441c6ace4e67b480cf13efc44abbc5a77670e74bc2c64a6a& https://cdn.discordapp.com/attachments/1417390884663726220/1418143696087679077/Vonage_SPI_fowarding.png?ex=68cd0cbc&is=68cbbb3c&hm=d82221428169b9f5801be96e2386d0a8b3916f0628ac8efadaf71e586bc4efc0&

We are reviewing the details of your request and will reach out to you when we have an update or if we need additional information.