I'm experiencing persistent transfer call failures and need technical assistance to identify the root cause. Despite following troubleshooting steps, transfers continue to fail at the platform level. Issue Summary: Transfer function executes successfully ("Transfer initiated" in logs) All calls end with "call.in-progress.error-transfer-failed" No outbound calls appear in Twilio console logs Problem occurs consistently across multiple test calls Configuration Details: Using Twilio phone number as SIP provider Transfer destination: +15625002833 SIP REFER enabled on Twilio trunk (per previous support guidance) Function configured correctly with proper destination parameter Call Logs Attached: Call ID: 6fe32c43-2e1f-4aff-a0d2-3c6e64f372ea (latest failure) Call ID: 69a35442-1cce-4da7-a68d-5524d96fcf79 (previous failure) Call ID: bbf10970-ec01-4ef6-8729-809121c6c84e (earlier failure) What I've Already Tried: Verified phone number format (+15625002833) Confirmed function parameters are correct Enabled SIP REFER on Twilio trunk Tested with multiple different call attempts What I Need: The current logs don't show SIP-level details. I need you to investigate: Are SIP REFER messages actually being sent to Twilio? What specific error response is Twilio returning? Is there a Vapi-Twilio integration issue causing the failures? The transfers fail after your platform reports "Transfer initiated," but before any call reaches Twilio. This suggests the issue is within Vapi's transfer processing, not the destination number or Twilio configuration. Please provide SIP-level debugging information or escalate to your engineering team for deeper investigation. Account Details: Org ID: 163cbd95-9a5b-48a2-b004-3728a6a4ae46 Using Twilio as telephony provider Thank you for your assistance.

Hey! To help track down this issue, could you share: \- The call ID \- When exactly this happened (the timestamp) \- What response you expected to get \- What response you actually got instead This would really help us figure out what went wrong!

@Praveen I'm having the same issue for SIP transfers. Here is a call-id: 783336b0-fd0c-4c2a-bee0-d3209c29badf

@User I'm having the same problem. Is there an update to this?

@User I'n having the same issue. My transfers are not working

Hey, thanks for sharing your details. Our team will look into it and get back to you soon with an update.

Hi, I am facing the exact same issue. my use case is that i want to make call to my customer and upon request i want the AI to transfer the call to a human agent but if the transfer fails for some reason then i want to reume the call with customer without ending the call. for this i am using transfer plan mode: warm-transfer-experimental call ID: 34a7d0d4-1748-46f3-a96a-4f9fa12d9f11 But right now the call when fails to transfer it ends with the error call.in-progress.error-transfer-failed.

Hi, I'm really sorry for the delay. I know this can be frustrating, and our team is looking into it. We'll get back to you with an update soon.