Warm transfer fail
# supportm
Mary
10/02/2025, 4:59 PMThe issue we’re running into is exactly because all the modes in Vapi right now send SIP REFER. Since Twilio/PSTN won’t honor REFER, the transfers never complete.
"id": "a09e2d89-c8ea-4f57-b813-d57b88d9b20f",
"createdAt": "2025-05-29T17:45:14.992Z",
"updatedAt": "2025-10-01T17:56:52.814Z",
"type": "transferCall",
"function": {
"name": "transfer_call_tool"
},
"messages": [
{
"type": "request-start",
"blocking": false
}
],
"orgId": "4d4894ae-9e63-435b-8d2d-d165e6c5d7dd",
"destinations": [
{
"type": "number",
"number": "+15127673628",
"message": "I’m transferring you now to a loan officer at Texas Star Loans {{location}}. ",
"callerId": "+19035517555",
"description": "when the {{location}} is longview",
"transferPlan": {
"mode": "warm-transfer-say-summary",
"sipVerb": "refer",
"summaryPlan": {
"enabled": true,
"messages": [
{
"role": "system",
"content": "Please provide a short summary of the call for the loan officer.\n"
},
{
"role": "user",
"content": "Here is the transcript of the call: {{transcript}}"
}
],
"timeoutSeconds": 10,
"useAssistantLlm": false
}
},
"numberE164CheckEnabled": true
},
{
"type": "number",
"number": "+19036386940",
"message": "I’m transferring you now to a loan officer at Texas Star Loans {{location}}. ",
"callerId": "+19035517555",
"description": "when the {{location}} is mineola",
"transferPlan": {
"mode": "warm-transfer-say-summary",
"sipVerb": "refer",
"summaryPlan": {
We have six phone number all the same sipVerb : refer
I think that’s what vapi gave me as default
Mary
10/02/2025, 5:00 PMI tried separating all the phone number into six tool , still the same
And now I use only one tool adding all the destination number to only a tool
Mary
10/02/2025, 5:01 PM@User @User
Mary
10/04/2025, 6:32 PM@User @User
n
NIX
10/06/2025, 1:12 PMSup friend hope you doing great i know how frustrating that can be
NIX
10/06/2025, 1:12 PMPay me and i help you
NIX
10/06/2025, 1:12 PMhahaha thats how everybody is actually doing here
NIX
10/06/2025, 1:13 PMthe solutions is to make the agent use the sip instead of the number
NIX
10/06/2025, 1:13 PMsince you are using a Phone ( number ) directly no a sip twilio fails and everything fail
NIX
10/06/2025, 1:14 PMyou need to create a sip trunk in twilio and let the agent use the sip instead of the phone number
NIX
10/06/2025, 1:14 PMim not the best explaining but thats the soluting have the same problem
NIX
10/06/2025, 1:15 PMUse this guide from twilio that for me was the one that help me the most ( you wil need to read the vapi also)
https://docs.retellai.com/deploy/twilio
NIX
10/06/2025, 1:15 PMvapi need to fix this documentation or improve it
m
Mary
10/07/2025, 7:27 PMThanks man
n
NIX
10/08/2025, 12:36 PMother thing that you can try wich work better to me is, to get a second phone number to send the transfers there with an extension number and create a twilio function to redirect based in the extension number that the agent put
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