Currently my live agents are not reporting any calls being transferred, despite seeing successful agent-transferred-call ended reasons. Initial Call ID Example: ce85c0b6-bd28-4eb6-be99-e0d3b65e7547 Here are the redacted Twilio logs for the attempted forward: Request URL = https://api.vapi.ai/twilio/twiml?verb=gather&text=This+call+is+being+transferred+from+the+agent.&timeout=15 Parameters = Called "+[transfer number]" ParentCallSid "[parent call sid]" ToState "NC" CallerCountry "US" Direction "outbound-dial" CallerState "NJ" CalledVia "+[call via number]" ToZip "" CallSid "[call sid]" To "+[transfer number]" CallerZip "07076" ToCountry "US" CalledZip "" ApiVersion "2010-04-01" CalledCity "" CallStatus "in-progress" From "+[originally dialed number]" AccountSid "[account sid]" CalledCountry "US" CallerCity "CRANFORD" ToCity "" FromCountry "US" Caller "+[originally dialed number]" FromCity "CRANFORD" CalledState "NC" ForwardedFrom "+[twilio number]" FromZip "07076" FromState "NJ" Response Body = This call is being transferred from the agent. #transfer-tool

Thanks for sharing the logs. To help narrow down the issue, can you confirm if your transferCall tool configuration includes the required

"destination"

property with the external number in E.164 format, and if SIP REFER is enabled on your SIP trunk? This is a common cause of silent transfer failures in Vapi setups. 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)

Yes, the transfer to number is in valid E.164 format. How can I verify SIP Refer in my Twilio account?

Hi Dr House, To troubleshoot the issue of call transfers dropping, follow these steps: 1. **Check Call Ended Reason**: - Use the API to fetch the call details and look at the

endedReason

. If it's not

assistant-forwarded-call

, review the assistant configuration. [Here is the detailed guide on how to do this.](https://docs.vapi.ai/phone-calling/transfer-calls/debug-forwarding-drops) 2. **Server Message Configuration**: - Ensure your server isn't overriding Vapi's call control. If "phone-call-control" is present in

serverMessages

, consider removing it. 3. **Phone Call Provider Bypass**: - Verify

phoneCallProviderBypassEnabled

is set to

false

for Vapi to handle call control. 4. **Transfer Scenario Compatibility**: - Check if your transfer scenario is supported. For instance, web-to-phone transfers are not supported. 5. **Analyze Telephony Provider Logs**: - If the call was forwarded successfully but then dropped, investigate using your telephony provider's logs with the

phoneCallProviderId

. 6. **SIP Packet Analysis (if applicable)**: - Use Wireshark to ensure

REFER

packets were sent and check for any error responses from the SIP provider. These steps should help identify and resolve the call drop issue during transfers.

I have created my Elastic SIP in Twilio by following the instructions outlined here: https://docs.vapi.ai/advanced/sip/twilio However, I did not do the section "Create a SIP Trunk Credential" as I had previously already added the three phone numbers from my Twilio account via the Vapi dashboard that are now located in the SIP. Is that going to be a problem?

We are looking into this some more and will provide an update shortly