VAPI•4mo ago

Dynamic Transfer Tool with properties does not work

From what I can tell, whenever a transfer tool includes any properties, the

transfer-destination-request

transfer-destination-request

webhook never fires. Instead, the assistant
immediately transfers the call to a default/random SIP destination.

For example:

{
"type": "transferCall",
"function": {
"name": "transfer",
"parameters": {
"type": "object",
"properties": {
"reasonForCalling": {
"description": "The reason the customer is calling. If not sure, use 'other'.",
"type": "string",
"enum": ["parts", "service", "other"],
"default": "other"
}
},
"required": []
},
"description": "Use this tool when transferring a call."
},
"messages": [{ "type": "request-start", "blocking": false }],
"destinations": []
}

Even when configured exactly as shown in your documentation
(see: https://docs.vapi.ai/assistants/examples/support-escalation),
the assistant skips the webhook and tries to transfer directly to

sip:parts@mysipuri.com

sip:parts@mysipuri.com

sip:parts@mysipuri.com

sip:parts@mysipuri.com.

---

Is this expected behavior, or has the

transfer-destination-request

transfer-destination-request

webhook
simply not been tested in SIP environments?

Vapi Support BotAPP•9/10/25, 7:17 PM

It appears that adding custom properties to the functionfunction object in your dynamic transfer tool may not be supported and can prevent the
transfer-destination-request
transfer-destination-request
webhook from firing. According to the documentation, the recommended approach is to define the transfer tool with an empty

destinations

destinations

array and no extra properties in the functionfunction object:

{
  "type": "transferCall",
  "destinations": [],
  "function": { "name": "dynamicDestinationTransferCall" }
}

{
  "type": "transferCall",
  "destinations": [],
  "function": { "name": "dynamicDestinationTransferCall" }
}

Try removing custom properties from the functionfunction and use only the minimal structure above to ensure the webhook is triggered as expected.
See documentation

Source:

Dynamic Call Transfers

⤵️ Mention @Vapi Support Bot for follow-ups 🐥

VapiAPP•9/12/25, 4:11 PM

Hello,Thanks for reaching out to us.We are sorry for the inconvenienc

Since you've referenced the support escalation documentation and are seeing behavior that differs from what's documented, this could be either:

A bug in how the transfer tool interacts with SIP destinations
An undocumented limitation of the transfer-destination-request webhook in SIP environments

Given that you're seeing unexpected behavior even when following the exact configuration from the documentation, I recommend:

Testing without any properties in the transfer tool to confirm the webhook works in that case
Documenting the specific SIP transfer behavior you're seeing
Reporting this as a potential issue to support, including:
- Your full transfer tool configuration
- The expected webhook behavior
- The actual transfer behavior you're observing
- Your SIP environment details

This will help determine if this is a bug or if there are undocumented limitations that need to be clarified in the documentation

If this doesn’t resolve the issue, please let us know and we’ll be happy to step in and assist further.

instant-harlequin•10/9/25, 9:24 PM

hello @Duckie @Vapi this is a bug. I've confirmed that I'm also experiencing the same issue. This bug is particularly egregious because it takes away the whole purpose of a dynamic transfer tool. Is there an ETA on the fix? thanks

Vapi Support BotAPP•10/9/25, 9:25 PM

There is currently no documented ETA for a fix to this bug. As a workaround, define your dynamic transfer tool with an empty

destinations

destinations

array and no custom properties in the functionfunction object to ensure the

transfer-destination-request

transfer-destination-request

webhook fires:

{
  "type": "transferCall",
  "destinations": [],
  "function": { "name": "dynamicDestinationTransferCall" }
}

{
  "type": "transferCall",
  "destinations": [],
  "function": { "name": "dynamicDestinationTransferCall" }
}

If you need to track the bug or request an update, consider reporting your case to Vapi support with your configuration and environment details.

Source:

Dynamic Call Transfers

VapiAPP•10/13/25, 7:16 PM

Hi falseVacuum,

It seems you're encountering issues with the transfer tool. Here's a method to add a transfer destination to the tool:

Ensure the CreateTransferCallToolDTOCreateTransferCallToolDTO object includes a
```
type
```
```
type
```
with the value
```
transferCall
```
```
transferCall
```
.
Specify the transferModetransferMode within TransferDestinationAssistantTransferDestinationAssistant if transferring to an assistant, and use rolling-historyrolling-history or swap-system-message-in-historyswap-system-message-in-history as options.
If transferring to a phone number, include TransferDestinationNumberTypeTransferDestinationNumberType.

For further assistance with the setup of transfer tools, ensure that all required fields in the TransferPlanTransferPlan and CreateTransferCallToolDTOCreateTransferCallToolDTO are correctly filled as indicated in the API documentation.

Feel free to reach out if you need more details on this process.

Dynamic Transfer Tool with properties does not work

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