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Calls not being transferred by AI Agent.
# support
s
Hi, I’ve configured a "transfer_call_tool" in my assistant, which is being triggered correctly based on the call transcript and tool logs. However, despite the assistant reporting the transfer and the destination being correctly defined in E.164 format, the call is never received at the destination — and no SIP or PSTN activity is recorded in Twilio or my Dialpad console. I've tested with a Twilio number, Dialpad number, and my personal mobile number. However in all cases the assistant speaks the transfer message and the tool logs confirms the execution but no actual calls are placed.
s
Can you check the .pcap file for the actual error? This most likely is a configuration issue. transfer call is bein rejected either at SIP or VAPI end.
s
Thank you for the suggestion Just to confirm, how do I access the file?
s
My bad. I was helping someone with signal wire cloud and wrote that message here. Please ignore my last message. Please access SIP call log in twilio console. You will find it in Call SID under Call logs. And tell me the error with error code.
s
Hi Surbat. Thank you for the clarification. Unfortunately the only log available on Twilio is the log when I call the AI Agent's number. No logs are recorded when the AI agent attempts to forward the call back to a different Twilio number.
s
@psbhullar Please help here.
p
This issue is in transfer call tool only? while you are trying to trigger the transfer call, It seems likely that the issue with the "transfer_call_tool" in your Vapi assistant is due to a configuration error, possibly with the tool's destinations or Twilio integration.
c
It doesn't initiate a real call, so you must manually create an outbound call via Twilio or Dialpad and bridge it usually via a conference or use the WebSocket 
controlUrl
to trigger the transfer otherwise, no SIP/PSTN activity will occur..
s
Hi @psbhullar, yes. I also tried to make a different tool with the same function, however I am experiencing the same error. I basically configured these tools on the tools console of Vapi. https://cdn.discordapp.com/attachments/1387999384498606161/1389773939626082414/image.png?ex=6865d757&is=686485d7&hm=f3b57cbeb7c3b164f5c754574eba6f81d3375a54a785cc7ef220beba1355d150&
After some investigations, we've found that our Twilio Number is getting a 32218 - SIP: Transfer not allowed every time we try to transfer the call from our AI Agent. We've fixed this error by enabling call forwarding on our Twilio SIP service Trunk. However, we are now receiving this new error on Twilio. https://cdn.discordapp.com/attachments/1387999384498606161/1389940036853563433/image.png?ex=68667208&is=68652088&hm=9d0fa04539666979b97cdadcc9c296361daca6fb20a1463582fd8e666d4ee7ff&
c
Could you send me the Twilio logs if possible? You can either post here or send as DM
s
Hello Kyle, Which specific details from the logs do you need?
c
Hey! To help track down this issue, could you share: - The call ID This would really help us figure out what went wrong!
s
Hi Shubham, Here are some call IDs for your reference d9801ee1-e32a-4090-96bc-f9f006dcbdf4 5cf7fce0-f90c-4cc4-942e-d394bd2381fc
c
Hey Smart Suites, Thanks for reaching out! We're currently swamped with a bunch of tickets and it's taking us longer than usual to get back to everyone. I know waiting isn't fun, but we want to make sure we give your issue the attention it deserves rather than rushing through it. We'll circle back with you soon to get this sorted out.
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{
  "callId": "5cf7fce0-f90c-4cc4-942e-d394bd2381fc",
  "endedReason": "assistant-forwarded-call",
  "callType": "inboundPhoneCall",
  "phoneCallTransport": "sip",
  "destinationDetails": {
    "type": "number",
    "number": "+61489275445",
    "message": "Transfer the call to a human agent",
    "transferPlan": {
      "mode": "blind-transfer",
      "sipVerb": "refer"
    },
    "numberE164CheckEnabled": true
  },
  "phoneCallProviderId": "c5fe6239-855b-473c-8aaa-95ee1642322e",
  "phoneCallControlEnabled": false,
  "phoneCallProviderBypass": false,
  "pcapFileUrl": "https://storage.vapi.ai/5cf7fce0-f90c-4cc4-942e-d394bd2381fc-1751457367215-ae15640f-0114-4556-b9b8-4040e3f962af-sip.pcap",
  "userGuidance": "Check PCAP file for SIP REFER method. If REFER packet exists with 202 Accepted response, transfer was successful."
}
Copy code
{
  "callId": "d9801ee1-e32a-4090-96bc-f9f006dcbdf4",
  "endedReason": "assistant-forwarded-call",
  "callType": "inboundPhoneCall",
  "phoneCallTransport": "sip",
  "destinationDetails": {
    "type": "number",
    "number": "+61489275445",
    "message": "Transfer the call to a human agent",
    "transferPlan": {
      "mode": "blind-transfer",
      "sipVerb": "refer"
    },
    "numberE164CheckEnabled": true
  },
  "phoneCallProviderId": "66ea6f1d-73cd-4bb4-8211-a567939e7ff8",
  "phoneCallControlEnabled": false,
  "phoneCallProviderBypass": false,
  "pcapFileUrl": "https://storage.vapi.ai/d9801ee1-e32a-4090-96bc-f9f006dcbdf4-1752128316719-c2d89c81-a44c-41cc-b724-623ca9716be3-sip.pcap",
  "userGuidance": "Check PCAP file for SIP REFER method. If REFER packet exists with 202 Accepted response, transfer was successful."
}
Hey SmartSuites! These are our call forwarding analysis for the two shared call IDs. The call has been successfully forwarded from us. As you can see in the shared analysis, you have to check with your telephony why they are rejecting these forwarded calls and if they require something to be tweaked for call forwarding, we can discuss about it.
s
Hi Shubham, Thank you for the confirmation. I've received information from Twilio support that the reason twilio rejects the call is because of the incorrect URL. Current URL:sip: @172.21.138.0:5060;transport=udp Correct URL should be:sip: @vapi-2-smartsuites.pstn.twilio.com I tried to change the URL by updating my transfer call tool, but Vapi is not allowing me. Is there another option where I can change the URL being passed by Vapi with the correct URL? Additionally, we'd like to confirm if this is a common issue between Vapi and Twilio, or is this an isolated case for us?
c
We are reviewing the details of your request and will reach out to you when we have an update or if we need additional information.
Hey Smart Suites, I sincerely apologize for the delay in our responses this week. We experimented with some process adjustments that didn’t work as intended, and unfortunately, this caused some disruptions. That’s entirely my responsibility. Just a quick note—our team is unavailable on weekends. However, if something urgent or critical comes up, feel free to reach out to me directly, and I’ll assist you. The support issues will be resolved in the coming weeks, and starting Monday, you can expect more consistent and improved support. Thank you so much for your patience and for continuing to stick with us!
s
Hi Shubham, good day! Do we have updates on our reported problem?
Hello Shubham, good day. Just checking in—do we have any updates on this concern? We’re hoping to resolve this urgently, as it’s been almost a month since the issue occurred. Looking forward to your update. Thank you!
c
Hi, First off, we want to sincerely apologize for the delay in getting back to you. We understand how frustrating it is to wait - especially when you're counting on us - and we owe you a clear explanation of what’s been happening and how we’re addressing it. Over the past few weeks, we've seen a significant increase in support requests. While this reflects exciting growth, it has also stretched our small team and exposed some real challenges in scaling our support operations. To improve your experience, we’ve taken a step back to reassess our approach. Here’s what we’re implementing: - Smarter Support Through Automation: We’re investing in our AI support systems to help you resolve issues more efficiently. Soon, our support bot will offer expanded capabilities, making it easier to access accurate, instant help—particularly for common or repetitive queries. - Expanding the Support Team: To meet growing demand, we’re adding 2–3 new team members focused on managing support volume and improving response times. - Prioritized SLAs for High-Usage Accounts: We’re introducing service level improvements for users who are growing with us: - Accounts with usage over 1,000 minutes/month will receive prioritized support. - For all general inquiries, we’re establishing a standardized 48-hour response time. We’re confident these steps will lead to faster, more reliable support and help us better serve you as you grow with us. Also, in case you still need help with this ongoing ticket, do let us know, and we will help you get this resolved as soon as possible. Thank you for your continued patience and for being part of our journey. Warm regards, Vapi Team
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