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Call fails after transfer_call tool started.
# support
t
I can successfully trigger the agent to call the transfer_call tool but after speaking the request started message, the call immediately ends.
v
Suggestion: Check that your 
transferCall
tool configuration includes a valid destination number and, if using a transfer plan, that the plan is correctly specified. For example:
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json
{
  "type": "transferCall",
  "destinations": [
    {
      "type": "number",
      "number": "+1234567890",
      "message": "I am forwarding your call to Department A. Please stay on the line."
    }
  ]
}
If the call still ends immediately, review your call logs for errors and ensure the destination is reachable and correctly formatted. Source: - [Vapi Call Forwarding Documentation](https://docs.vapi.ai/call-forwarding)
t
@Vapi Support Bot i've configured both SIP and assistant destinations. The api logs result in 200 responses.
v
Suggestion: Please double-check that your SIP transfer destination is using the correct SIP URI format and that SIP REFER is enabled on your provider. For example:
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json
{
  "type": "transferCall",
  "destinations": [
    {
      "type": "sip",
      "sipUri": "sip:14039932200@sip.telnyx.com",
      "message": "Connecting your call via SIP."
    }
  ]
}
If SIP REFER is not enabled, the transfer will fail and the call may end immediately. [See documentation for details](https://docs.vapi.ai/advanced/sip/sip-trunk#sip-refer-call-transfer) Sources: - [Vapi Call Forwarding Documentation](https://docs.vapi.ai/call-forwarding) - [Vapi SIP Trunking and SIP REFER](https://docs.vapi.ai/advanced/sip/sip-trunk#sip-refer-call-transfer)
t
@Vapi Support Bot what about using the assistant destination?
v
Currently, the Vapi documentation does not provide a concrete example or explicit configuration for using the 
assistant
type as a transfer destination in the 
transferCall
tool. While dynamic call transfers are described as supporting transfers to "other assistants," the required payload and troubleshooting steps for this use case are not detailed. I recommend reaching out to Vapi support or consulting the [dynamic call transfers documentation](https://docs.vapi.ai/calls/call-dynamic-transfers) for the latest updates on assistant-to-assistant transfers. Source: - [Dynamic Call Transfers Documentation](https://docs.vapi.ai/calls/call-dynamic-transfers)
p
Hey! To help track down this issue, could you share: - The call ID
t
Hi Kyle, i managed to solve it via transfers to assistants linked in Squads. But i've realised that once i assign the "transfer_call" tool to an assistant, i'm unable to start a web call directly from the assistant menu itself. I keep running into "destination (assistant name) not found". This error goes away when i remove the call transfer tool from the assistant. Is this expected behaviour? Sometimes i want to test the agent individually instead of in the squad setup.
v
Yes, this is expected behavior: When you assign a 
transferCall
tool with assistant destinations, the assistant is designed to operate within a Squad context for assistant-to-assistant transfers. Attempting to start a web call directly from the assistant menu (outside of a Squad) will result in a "destination (assistant name) not found" error. To test the agent individually, temporarily remove the transfer tool or use the Squad setup for full transfer functionality. For more details, see the [Squads documentation](https://docs.vapi.ai/squads) and [Squads example](https://docs.vapi.ai/squads-example). Sources: - [Squads documentation](https://docs.vapi.ai/squads) - [Squads example](https://docs.vapi.ai/squads-example)
v
Message marked as helpful by @timmmmmo! 🎉
p
No this is not the intended behavior, can you share the call_id so we can take a look?
t
Hi Shubham, i can't provide the call_id because it doesn't show up in the logs. Here's the error that i get when attempting to start a web-call from the UI. https://cdn.discordapp.com/attachments/1375861648715284520/1376582993333719111/image.png?ex=6835da51&is=683488d1&hm=7699009b61968c9be41e085ddce78cbda52f4fde13acdc6c4bc5b6e2aa6e1e36&
Here's the assistant IDs where it happens. (All of them have been assigned the transfer_call tool). d7c4b8fe-2cc1-4b5a-a3a7-2b31c86ed02d 7c2df9aa-2265-420f-8b7a-a9ab15533822 6ba4aa77-28cd-44b6-b83e-9b43b32c4e0b
and the id of the transfer_call tool -> f758bd88-bdaa-4642-920e-3a0d63048b65
v
To resolve the "Invalid Destination. Assistant 'ERS_Clinic_CN' Not Found" error when using assistant destinations in the 
transferCall
tool, ensure you are initiating the call within a Squad context where all assistant destinations are defined as squad members. For example, your squad configuration should look like:
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json
{
  "squad": {
    "members": [
      {
        "assistantId": "your-main-assistant-id",
        "assistantDestinations": [
          {
            "type": "assistant",
            "assistantName": "ERS_Clinic_CN",
            "message": "Transferring you to ERS Clinic."
          }
        ]
      },
      {
        "assistant": { "name": "ERS_Clinic_CN", ... }
      }
    ]
  }
}
Test your transfer flows using the Squad setup to avoid this error. [See Squads documentation for details.](https://docs.vapi.ai/squads) Sources: - [Squads documentation](https://docs.vapi.ai/squads) - [Squads example](https://docs.vapi.ai/squads-example)
To test an assistant with the 
transferCall
tool (using assistant destinations), you must initiate the call within a Squad context. Direct web calls from the assistant menu will result in an "Invalid Destination" error because assistant-to-assistant transfers require the Squad setup to resolve destinations. If you want to test the agent individually, temporarily remove the transfer tool or use a Squad for full transfer functionality. For more details, see the [Squads documentation](https://docs.vapi.ai/squads) and [Squads example](https://docs.vapi.ai/squads-example). Sources: - [Squads documentation](https://docs.vapi.ai/squads) - [Squads example](https://docs.vapi.ai/squads-example)
To test an assistant with the 
transferCall
tool (with assistant destinations), you must use the Squad setup. Direct web calls from the assistant menu will fail with "destination not found" because assistant-to-assistant transfers require all destinations to be defined as squad members. Actionable tip: For individual testing, temporarily remove the transfer tool or create a minimal Squad with just your assistant and a dummy destination. For more details, see the [Squads documentation](https://docs.vapi.ai/squads) and [Squads example](https://docs.vapi.ai/squads-example). Sources: - [Squads documentation](https://docs.vapi.ai/squads) - [Squads example](https://docs.vapi.ai/squads-example)
Thanks for sharing the assistant and tool IDs. To clarify your workflow: Are you looking to test assistant-to-assistant transfers outside of Squads (i.e., from the individual assistant menu), or is your main goal to enable transfers only within Squad-based calls? This will help determine if there’s a supported approach for your use case. Sources: - [Squads documentation](https://docs.vapi.ai/squads) - [Squads example](https://docs.vapi.ai/squads-example) - [Dynamic Call Transfers Documentation](https://docs.vapi.ai/calls/call-dynamic-transfers)
p
Can you recreate the assistant and assign it to an squiad?
squad\*
t
i had previously duplicated the assistant and faced the exact same issue.
v
Duplicating the assistant will not resolve the "Invalid Destination" error unless you initiate the call within a Squad context. To enable assistant-to-assistant transfers, make sure both the source and destination assistants are defined as squad members. Here’s a minimal Squad configuration example:
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json
{
  "squad": {
    "members": [
      {
        "assistantId": "your-main-assistant-id",
        "assistantDestinations": [
          {
            "type": "assistant",
            "assistantName": "ERS_Clinic_CN",
            "message": "Transferring you to ERS Clinic."
          }
        ]
      },
      {
        "assistant": { "name": "ERS_Clinic_CN" }
      }
    ]
  }
}
Test your transfer flows using this Squad setup to avoid the error. For more details, see the [Squads documentation](https://docs.vapi.ai/squads). Sources: - [Squads documentation](https://docs.vapi.ai/squads) - [Squads example](https://docs.vapi.ai/squads-example)
Duplicating the assistant will not resolve the "Invalid Destination" error. To enable assistant-to-assistant transfers with the 
transferCall
tool, you must initiate the call within a Squad context where all destination assistants are defined as squad members. Here’s a minimal Squad configuration example:
Copy code
json
{
  "squad": {
    "members": [
      {
        "assistantId": "your-main-assistant-id",
        "assistantDestinations": [
          {
            "type": "assistant",
            "assistantName": "ERS_Clinic_CN",
            "message": "Transferring you to ERS Clinic."
          }
        ]
      },
      {
        "assistant": { "name": "ERS_Clinic_CN" }
      }
    ]
  }
}
Action: Always use a Squad for these transfer flows—direct calls from the assistant menu will not work for assistant destinations. [See Squads documentation for more details.](https://docs.vapi.ai/squads) Sources: - [Squads documentation](https://docs.vapi.ai/squads) - [Squads example](https://docs.vapi.ai/squads-example)
To clarify and help resolve your issue: Are you aiming to enable and test assistant-to-assistant transfers only within Squad-based calls, or do you specifically need this functionality to work from individual assistant web calls (outside of Squads)? This will help determine if there is a supported approach for your use case. Note: Assistant-to-assistant transfers require a Squad context; direct web calls from the assistant menu will result in "Invalid Destination" errors if the transfer tool is present. For more details, see the [Squads documentation](https://docs.vapi.ai/squads). Sources: - [Squads documentation](https://docs.vapi.ai/squads) - [Squads example](https://docs.vapi.ai/squads-example)
To resolve the "Invalid Destination. Assistant 'ERS_Clinic_CN' Not Found." error, you must initiate your call within a Squad context where all destination assistants are defined as squad members. Here’s a minimal Squad configuration example:
Copy code
json
{
  "squad": {
    "members": [
      {
        "assistantId": "your-main-assistant-id",
        "assistantDestinations": [
          {
            "type": "assistant",
            "assistantName": "ERS_Clinic_CN",
            "message": "Transferring you to ERS Clinic."
          }
        ]
      },
      {
        "assistant": { "name": "ERS_Clinic_CN" }
      }
    ]
  }
}
Always use the Squad setup for assistant-to-assistant transfers; direct calls from the assistant menu will not work for this use case. [See Squads documentation for details.](https://docs.vapi.ai/squads) Sources: - [Squads documentation](https://docs.vapi.ai/squads) - [Squads example](https://docs.vapi.ai/squads-example)
p
Hey there! Just a heads-up: you can’t set a transfer tool to an assistant outside of squads. Only squads can handle transferring between assistants. If you try sending it to another squad outside of this setup, it won’t work. Also, if you’re thinking of transferring a web call to a phone number, that won’t fly either. Transfers to phone numbers only work with phone calls at the moment.
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