Call IDs: 9d57702f-7893-4612-834d-6baea813334a, 92fd1f84-0ecc-49c0-95eb-3e8ededf5df5, a563c715-44a3-4837-9879-778ab1fea411 We make outbound calls using the API and transient assistants (provide all assistant config via the create call API call). Trying to configure call transferring. It successfully calls the tool and reads the tool message "Transferring your call to {x}, please stay on the line..", and then just ends the call. I know the transfer destination phone number destination is valid. In the logs, ended reason says "Assistant forwarded call"

Check that your

transferCall

tool includes the required

destination

property and that your SIP trunk supports SIP REFER. If SIP REFER is not enabled or supported, the call will end after the transfer message. Here’s an example of the correct parameters section for your tool:

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 SIP provider supports SIP REFER for transfers, as Vapi does not support alternative SIP verbs for call transfers. [Reference: Vapi documentation and support](https://docs.vapi.ai/call-forwarding) Sources: - [Vapi documentation: call forwarding](https://docs.vapi.ai/call-forwarding) - [Vapi SIP Trunking Telnyx external number call forwarding troubleshooting (Discord)](https://discord.com/channels/1211482211119796234/1343963959421829172)

Hey! Can you check in your Twilio console log for this call? The call was forwarded successfully from our side but then it was rejected from the Twilio side with 403 forbidden. So I'll suggest you to check in Twilio console log for more details.