Suggestion: Make sure your transfer destination number is in E.164 format (e.g.,

+491234567890

for Germany) and that your transfer tool includes the required

destination

property. Here’s an example configuration for your transfer function:

json
"parameters": {
  "type": "object",
  "properties": {
    "destination": {
      "type": "string",
      "enum": ["+491234567890"], // Replace with your German number
      "description": "The destination to transfer the call to."
    }
  },
  "required": ["destination"]
}

Double-check this setup in your tool—incorrect number format or missing parameters are the most common reasons for transfer failures with Twilio SIP trunks and international numbers. Sources: - [Vapi documentation: call forwarding](https://docs.vapi.ai/call-forwarding) - [Debug call forwarding drops](https://docs.vapi.ai/phone-calling/transfer-calls/debug-forwarding-drops)

I can help you fix this. I’ve handled several Twilio SIP setups with German numbers before. Call transfer issues often come from SIP header handling, regional carrier restrictions, or missing “Allow SIP Refer” permissions. I’ll check your transfer flow and trunk config to pinpoint the cause. Could you confirm if you’re using Twilio Elastic SIP or PJSIP, and whether your trunk handles both inbound and outbound calls through the same domain? @rocket

Hi rocket, To help you with issues related to call transfers where the call is disconnected immediately after initiating the transfer, you can refer to some practical steps. The most common issues and resolutions are: 1. Verify `endedReason`: Use the [Debug call forwarding drops](https://docs.vapi.ai/phone-calling/transfer-calls/debug-forwarding-drops) guide to check logs and determine whether the call ended with

"assistant-forwarded-call"

. If yes, proceed to the next steps; otherwise, check assistant configuration. 2. **Check Call Logs**: Make a GET request to Vapi API with your Call ID to see why the call ended: -

assistant-forwarded-call

suggests the transfer was successful from Vapi's end. - If the transfer wasn't initiated, check your assistant's

serverMessages

configuration and remove

"phone-call-control"

if present. 3. **Telephony Provider Logs**: Ensure you use the

phoneCallProviderId

from Vapi's expected response to check your provider's logs (Twilio, Vonage, Telnyx) for errors during transfer. 4. **Configuration Validation**: Ensure

phoneCallProviderBypassEnabled

is set to

false

, and your destination numbers are verified, correctly formatted, and reachable. 5. **Scenario Support**: Verify the transfer scenario is supported, e.g., phone call to phone number is supported, but web call to phone number isn't. 6. **SIP Signaling (If applicable)**: If using SIP, download and analyze the SIP packets using Wireshark to see if REFER packets are being sent and accepted. Following these steps should help in identifying and resolving the issue. For more detailed changes and configurations, you can refer to our [Call Forwarding](https://docs.vapi.ai/call-forwarding) documentation for setting up transfers effectively.

hi, this is comprehensive explanation @User but this all https://docs.vapi.ai/phone-calling/transfer-calls/debug-forwarding-drops is about analysis of the call errors. How do I set my assistant behorehand configuration as { "assistant": { "serverMessages": ["status-update"] } } and { "phoneCallProviderBypassEnabled": false } if there is no such fields to enter in https://dashboard.vapi.ai/assistants dashboard

Thanks for getting back to us and updating us We’ll share an update as soon as more information becomes available. We appreciate your understanding and patience as we continue our investigation.