workflow ID: a43e4d98-fe6b-4f7e-b5d7-49ef72675053 1. Tried GPT 4.0, 4.1, 4.1 mini, 40 cluster no effect 2. Added & removed stop node after transfer call no effect. 3. Tried single prompt agent no workflow, call transfers still fail 4. Selected all the warm call transfer options/modes, and blind transfer with no effect 5. Added removed Enforce E164 format 6. Ensured the Phone Number is good its just my personal cell phone 7. Request Start Message Default, None, Custom no effect 8. Removed all spoken messages during for any and all stages of tool execution

Thanks for the detailed troubleshooting steps you've tried. To help diagnose why outbound call transfers are failing, could you please share the specific error message or log output you receive when a transfer attempt fails? This will help pinpoint the root cause and suggest the most effective solution. Sources: - [Vapi documentation: call forwarding](https://docs.vapi.ai/call-forwarding) - [Vapi SIP integration guide](https://docs.vapi.ai/advanced/sip/telnyx) - [Discord support thread](https://discord.com/channels/1211482211119796234/1343963959421829172)

Test Suite ID: 013b25ff-65aa-4544-b165-44a901e708c2

@B2 TheW There appears to be a serious misconception about Transfers in the VoiceAI world. When you do a warm transfer, that is operated via a

SIP Refer

- you always need to remember that a

SIP Refer

is a BEST EFFORT tool - which means, there are 100 different ways it can fail - and it is up to you to make sure to handle all these failure in a meaningful manner. This about it this way, a

SIP Refer

is a little like walking the streets of Manhatten, on your way to a specific address. On your way, you stop to buy a coke, and ask the guy at the register how to get to your destination. He gives you instructions, and off you go. If you get there, he doesn't know - NOR DOES HE CARE. That is similar to a

SIP Refer

, you ask the remote server to "connect you somewhere", but if it doesn't connect, it's up to you to handle that failure, no the remote server. What you are looking to do is a Supervised Transfer, which doesn't use

SIP Refer

but uses an external workflow, that can be monitored and adjusted as the workflow is executed. You are welcome to DM me for more details.

@Nir Simionovich (CEO@Cloudonix) im just trying to get a simple phone transfer.

I know, but this is the reality of the protocol

Synthflow call transfers are straight forward call transfers on VAPI were simple and straight forward last time i used them May 13 2025

@B2 TheW Trust me when I tell you that the same issues are reported on multiple AI platforms, even 11labs, ReTell, Synthflow, LiveKit - they all suffer from similar complaints. Last night I did a meetup in NY, for AI Agencies, talking specifically about these issues - of why Voice AI platforms are having so much trouble with transfers and other telephony related features, which you take for granted - but infact, are very complex to an AI to operate properly.

Oh rite yeah ok, i forgot that I was SIP trunking. This wasnt just a VAPI number, ok I need to go do some networking pcaps, twillio trunk work now

Hey! To help track down this issue, could you share: - The call ID This would really help us figure out what went wrong!