i am using transfer call tool still getting this error https://cdn.discordapp.com/attachments/1421381494798024704/1421381495049945160/Screenshot_2025-09-27_at_11.51.03_AM.png?ex=68d8d42c&is=68d782ac&hm=4cc5dd5529dd4de41652448ea71512a838a1c78248baef0ee4d636e4df869935&

Try this: Double-check that your

transferCall

tool includes the required

destination

parameter in E.164 format and that SIP REFER is enabled with your provider. Here’s an example configuration for the parameters section:

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

If the issue persists, verify with your provider that SIP REFER is supported and enabled for your trunk. Sources: - [Vapi documentation: call forwarding](https://docs.vapi.ai/call-forwarding) - [Vapi SIP Trunking Telnyx external number call forwarding troubleshooting](https://discord.com/channels/1211482211119796234/1343963959421829172)

@WhilpashH I'm not a VAPI employee - but I'm interested in your report. Are you using BYO SIP trunking?

Was this during a web call? Also please provide the call id