VAPI•14mo ago

Extension not working on transfer when responding to 'assistant-request'

We are trying to build a feature that can transfer the call if there are any errors or if the system is offline, or phone number is blocked. We are going through the docs (https://docs.vapi.ai/api-reference/webhooks/server-message#response).
It is transfering/forwarding the call successfully, but the extension is not.
The extension works great when using the 'transferCall' functionCall. But not in this part.
This is an example of the response to 'assistant-request':
{"messageResponse":{"destination":{"type":"number","number":"+19999999999","extension":"1","numberE164CheckEnabled":true}}}
We've tried with different variations of numberE164CheckEnabled boolean.
Just wanted to see if we are missing something.
This is a sample callId:
73e83cba-4ecb-4a30-abe6-c308940de85c

Vapi

Server Message — Vapi

Vapi•11/1/24, 3:41 PM

@Chris
It's great to hear that you're successfully transferring calls with the transferCalltransferCall function. If the extension is not being transferred correctly when responding to an assistant-requestassistant-request, it might be due to how the destination is being handled by the system after the transfer request.

The numberE164CheckEnablednumberE164CheckEnabled boolean is intended to enable or disable the E.164 formatting check for the provided phone number. This should not affect the transfer of the extension. The extension should be transferred along with the call as long as the destination system supports and correctly interprets the extension parameter.

Here are a few things you can check or try:

Destination System Compatibility: Ensure that the destination system (the one receiving the transferred call) is capable of handling the extension parameter. Some systems might require additional configuration to recognize and route calls based on extensions.
Parameter Formatting: Double-check the formatting of the extension parameter in your response. It should be a string and part of the destinationdestination object as you've shown.
Documentation and Examples: Review the VAPI documentation for any examples or additional parameters that might be required for transferring extensions.
Support and Logs: If you've confirmed the above and it's still not working, consider reaching out to VAPI support with logs and details of your implementation. They might be able to provide insights specific to your case.

If you've tried different variations of the numberE164CheckEnablednumberE164CheckEnabled boolean and it's not affecting the extension transfer, it's likely not related to the issue. The focus should be on how the extension is being processed after the call is transferred.

If you need further assistance or if you'd like me to perform any specific actions, please let me know!

Vapi•11/1/24, 3:41 PM

You can continue this conversation by mentioning me in the message.

VVapi You can continue this conversation by mentioning me in the message.

VapiAPP•11/1/24, 3:42 PM

Got it. Tagging @Vapi Team for additional help.

Sspecific-silver We are trying to build a feature that can transfer the call if there are any err...

dangerous-fuchsia•11/2/24, 4:08 AM

@Chris can you check call id again and try setting numberE164CheckEnabled to false.

Ddangerous-fuchsia @Chris can you check call id again and try setting numberE164CheckEnabled to fal...

specific-silverOP•11/4/24, 3:34 PM

We've tried adding the callerId also and numberE164CheckEnabled to false;
{"messageResponse":{"destination":{"type":"number","callerId":"+19802943076","number":"+16504415689","extension":"1","numberE164CheckEnabled":false}}}
Latest test callId: 0813f07d-93fa-4afb-9a49-5e13854cf971

dangerous-fuchsia•11/5/24, 3:19 PM

Hey @Chris sorry for the overlook, the assistant-requestassistant-request server event is for assistants only you cannot transfer the call using this server event. Instead you need to return the assistant and instruct the assistant to speak first with firstMessageMode and intitate the call transfer.

specific-silverOP•11/5/24, 3:51 PM

Ok I understand. Will the LLM continue with the transfer or will it expect user input?

Sspecific-silver Ok I understand. Will the LLM continue with the transfer or will it expect user ...

dangerous-fuchsia•11/5/24, 9:55 PM

Depends upon firstMessageMode, if you use modelGeneratedMessage then both firstMessage and tool can be called altogether.

Ddangerous-fuchsia Depends upon firstMessageMode, if you use modelGeneratedMessage then both firstM...

specific-silverOP•11/8/24, 6:23 PM

Excellent! That did it! Thanks for your help!

Ddangerous-fuchsia Hey @Chris sorry for the overlook, the `assistant-request` server event is for a...

colossal-harlequin•10/10/25, 1:07 PM

I have been using it for blind transfer like this and it works:

'messageResponse' => [
"destination" => [
"type" => "number",
"number" => "+14077031234"
]
]

colossal-harlequin•10/10/25, 1:07 PM

But when I try to use a transfer plan it forwards but does not execute the transferplan

'messageResponse' => [
"destination" => [
"type" => "number",
"number" => "+14077031234",
"transferPlan" => [
"mode" => "warm-transfer-experimental",
"transferAssistant" => [
"firstMessage" => "Hello, I have a customer on the line. Are you available to take this call?",
"firstMessageMode" => "assistant-speaks-first",
"maxDurationSeconds" => 120,
"silenceTimeoutSeconds" => 30,
"model" => [
"provider" => "openai",
"model" => "gpt-4o",
"messages" => [
[
"role" => "system",
"content" => "You are a transfer assistant designed to facilitate call transfers..."
]
]
]
]
]
]
]

colossal-harlequin•10/10/25, 1:13 PM

Is this a limitation for assistant-request? in the docs it is mentioned that transferPlan is supported in https://docs.vapi.ai/api-reference/webhooks/server-message#response.body.messageResponse.AssistantRequest.destination.NumberTransferDestination.transferPlan.mode

Server Message | Vapi

Extension not working on transfer when responding to 'assistant-request'

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