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Transfer errors
# ❓・bug-report
s
We are getting the following error from the transfer tool: "Transfer call cannot be completed, probably don't have the permission to perform the transfer.. Please inform the customer that the transfer did not go through and offer to try again or assist them directly." The tool is configured to make cold transfers with SIP REFER and no custom headers.
This started happening today
s
hello
which telephony provider are you using?
s
Twilio
Here is a more detailed error message: error: Error transferring call, SIP status code: 403 SIP error category: telephony_provider_permission_denied Error: twirp error unknown: unexpected status from INVITE response: sip status: 403: Caller ID is unauthorized. A Valid Caller ID is either a DID you have purchased from Twilio or a verified Caller ID.
o
Can you share the call id
But this usually happens if you have a call transfer with Display as "user's number" try make it to display as Retell's number
s
Yes - call_588f6ca085c584794a9373c8191
We need to preserve the caller's number for our use case
Performing a cold transfer has worked so far
o
So warm transfers with the user's number are supported retell-twilio numbers , for custom telephony you have to get permission from your provider because they are the one who preventing it.
s
We are doing a cold transfer
s
twillo only allows as caller id if the number is verified from the provider but your customer number is not verified with the provider so it is blocking you have three option in cold transfer use Retell Agent's number as caller id or switch to warm transfer or Configure SIP Header Rules in Twilio to override caller ID with a verified number
s
We have switched to retell-twilio number. What do we enter in the built in tool dialog to make transfers work with displaying the caller's nuymber on the transferee side?
s
then you can use caller id in cold transfer
s
What broke this? The same approach we have been using has worked for weeks.
s
so you were using cold transfer with caller id and its working fine?
s
Yes
It was working fine yesterday
@Shah - support @ Retell AI Could you shed some light on what changed and what we are supposed to set up on the Twilio side to be able to use the SIP Trunk functionality? It's not really feasible to have to migrate the phone numbers of dozens of customers without knowing the root cause of this. Something has had to change around 11:03UTC - the time when we first saw this breaking.
s
you’ll need to contact Twilio directly to investigate why this is happening.
s
We are noticing a difference in the transfer tool dialog for our agents in production vs. when creating a new agent. Here is how existing agent's dialog looks like: https://cdn.discordapp.com/attachments/1464343679673172039/1464376183155327231/image_24.png?ex=69753e18&is=6973ec98&hm=2a65d2b4d3aade1c6be1547ba50fb80609e18597495e85b37022031cc0259f35&
Did any of the defaults change under the hood? Notice that new bots can choose the display name but we cannot do that for existing bots.
c
you're getting this error because it's sent with sip invite, you need to use refer
s
Thank you. We were using cold transfers with SIP REFER when things broke. We found out that if we manually switch to SIP INVITE and then back to the same settings with SIP REFER, things work.
However if we deploy using the API, this is not always reliable.
This seems like a Retell issue, please check on your end and advise
Here is a call ID with failed transfer: call_4bab6297adb620b35320fc3e70a Here is a call ID in which transfers succeeded after we manually touched the transfer logic to INVITE and back to REFER: call_74d5477dac466add316dbb7b4bc
The sequence that worked was "sip invite" - save -publish , "sip refer" - save - publish manually in the Web portal
s
ok I have shared it with the team. Will let you know once get reply
f
o
there was a recent deprecation , please check this https://docs.retellai.com/deprecation-notice/1-26-2026
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