Call ID- e06f6284-7b6d-4ba2-880c-203ed7beee49 I am attempting to transfer the user from the agent to a phone number via the Assistants Page - I have tried creating a tool transfercall. and applying it to the agent - I have tried using just predeifned forwarding number - I have tried combination of both. - Call logs show unknown error so I don't have much to go off of. - I have tried transferring to Twilio number, Vapi number, and my cell. - I only have success if doing it from the Phone Numbers Page manually - No logs in Twlio, so it doesn't appear to be making it there. Happy to dig further, but could use some help please. Call analysis shows: *call_analysis: { key_topics: [ 0: "Call transfer" ] call_outcome: "Incomplete due to unknown error" call_purpose: "Call transfer request" user_sentiment: "Neutral" } }* Call Messages Show: { "role": "tool_calls", "time": 1747724681559, "message": "", "toolCalls": [ { "id": "call_MnPI4q9SEFvM1pM8nl0MrCDB", "type": "function", "function": { "name": "transferCall", "arguments": "{\"destination\": \"+1520xxxxxxx\"}" } } ], "secondsFromStart": 10.165 } { "name": "transferCall", "role": "tool_call_result", "time": 1747724682954, "result": "Success.", "toolCallId": "call_MnPI4q9SEFvM1pM8nl0MrCDB", "secondsFromStart": 11.56 }

Suggestion: Check that SIP REFER is enabled on your SIP trunk provider (e.g., Telnyx), as Vapi requires SIP REFER for call transfers from the Assistants page. If it's not enabled, transfers will silently fail or show unknown errors. Action: - In your SIP provider's portal, ensure SIP REFER is enabled for your trunk. - If using Telnyx, confirm with their support that SIP REFER is active. - After enabling, test the transfer again from the Assistants page. If SIP REFER is already enabled and the issue persists, review your transferCall tool configuration to ensure the "destination" parameter is set correctly and matches the E.164 format (e.g., "+1520xxxxxxx"). [Reference: Vapi SIP Trunking & Call Forwarding Docs](https://docs.vapi.ai/advanced/sip/sip-trunk#sip-refer-call-transfer) Sources: - [Vapi SIP Trunking Documentation](https://docs.vapi.ai/advanced/sip/sip-trunk#sip-refer-call-transfer) - [Vapi Call Forwarding Documentation](https://docs.vapi.ai/call-forwarding) - [Vapi Discord Support Thread](https://discord.com/channels/1211482211119796234/1372460612499804270)

You can't transfer a call from web call. You need to do it from telephony provider.