I have this tool used for transfering Calls to a SIP address

{
  "id": "60d07d45-531d-4b3e-9b42-df196102c16d",
  "createdAt": "2025-01-30T22:08:46.817Z",
  "updatedAt": "2025-01-31T15:57:41.185Z",
  "type": "transferCall",
  "function": {
    "name": "transferCall",
    "strict": true,
    "description": "used to transfer calls",
    "parameters": {
      "type": "object",
      "properties": {
        "destination": {
          "type": "string"
        }
      },
      "required": [
        "destination"
      ]
    }
  },
  "messages": [
    {
      "type": "request-start",
      "content": "I'll transfer you to someone who can help."
    }
  ],
  "orgId": "8e0c0a52-d82b-49dc-af03-a5023b63c6cf",
  "destinations": [
    {
      "type": "sip",
      "sipUri": "sip:[MY_EXTENTION]@mypbxadmin.com",
      "message": "Transferring your call to Sal now",
      "transferPlan": {
        "mode": "blind-transfer-add-summary-to-sip-header",
        "sipVerb": "refer",
        "summaryPlan": {
          "enabled": true,
          "messages": [
            {
              "role": "system",
              "content": "Provide a very brief 1-3 sentence summary of the key points from this call."
            },
            {
              "role": "user",
              "content": "Here is the transcript:\n\n{{transcript}}\n\n"
            }
          ]
        }
      }
    }
  ]
}

I downloaded blink and confirmed I can make SIP calls to the same sipUri established in this tool. However, when vapi executes this tool, webhook reports "result": "Success.", but I get an immediate hangup. I tried mimicing the SIP header info used from blink originally, but found that "blind-transfer-add-summary-to-sip-header" was probably a better approach. I've tried quite a bit. I don't manage our SIP system @mypbxadmin.com. Is it possibly a firewall issue? Tool Call ID: call_cmtRyvZL9PSujtb8aPTSIZ93 Call Id: 7d8ac106-8f90-4bfe-81a0-a8db0bacafd5

HeySal Thank you for creating the ticket! A member of our team will reach out to you shortly.

@Sal It sounds like you've done a thorough job in setting up and testing the call transfer tool with VAPI. Since the webhook reports a "Success" result but you experience an immediate hangup, there could be several reasons for this issue, including configuration on the SIP system, network issues, or compatibility problems between the VAPI transfer method and your SIP system. Given that you don't manage the SIP system at mypbxadmin.com, it's possible that the issue lies there. A firewall issue is one possibility; SIP ALG (Application Layer Gateway) settings or other firewall configurations could be interfering with the SIP messages. It's also possible that the SIP system requires specific headers or settings that are not being provided by the VAPI tool. Here are a few steps you can take to troubleshoot this issue: 1. **Check Firewall and Network Configuration**: Ensure that the firewall is properly configured to allow SIP traffic and that there are no blocks on the ports used by SIP. 2. **SIP System Compatibility**: Verify with the administrator of the SIP system at mypbxadmin.com if there are any specific requirements for transferring calls, such as expected headers, authentication, or supported SIP methods. 3. **Logs and Error Messages**: Request logs from the SIP system to see if it provides any error messages or clues as to why the call is being disconnected immediately after the transfer attempt. 4. **Contact Support**: If the issue persists and you're unable to identify the cause, it may be helpful to contact the support team for VAPI and provide them with the Tool Call ID and Call ID. They might be able to offer more insight or assist with further troubleshooting. If you'd like, I can assist you in contacting support with the relevant details. Would you like me to do that?

Ok, so I set up my own sip server using asterisk and made a public sip uri and disabled all firewalls on the server running it. I confirmed I can reach it from 2 different networks. However Vapi just hangs up immediately, server doesnt even see the inbound connection. Same SIP uri.

Hello brother, can I DM you... Wanted to make enquiry about sip trunk?

@Sal Unfortunately, Vapi does not technically support PSTN to SIP transfers. However, you may proceed with SIP to SIP transfers or SIP to PSTN transfers instead.

sip