I'm using this with my custom LLM. So far, the transfer and all happens well. However, if the number to which the conversation is being transferred declines the call, or doesn't pick up, the fallback does not seem to work. This is what my config looks like when sent to the conversation's control URL { "type": "transfer", "destination": { "type": "number", "number": phone_number, "callerId": '{{phoneNumber.number}}', "transferPlan": { "mode": "warm-transfer-experimental", "holdAudioUrl": "https://file.mp3", "summaryPlan": { "enabled": True, "messages": [ { "role": "system", "content": "Please provide a summary of the call." }, { "role": "user", "content": "Here is the transcript:\n\n{{transcript}}\n\n" } ] }, "fallbackPlan": { "message": "It seems the person is currently busy or on another call. Can I take a message?", "endCallEnabled": False } } } }

Hi there, Thank you for your message. Our team is currently out of the office. We operate Monday through Friday, from 9:00 AM to 8:00 PM Pacific Standard Time (PST). We’ll get back to you as soon as possible during our normal business hours. If your message is urgent, please mark it accordingly or include “URGENT” in the subject line, and we’ll do our best to respond promptly. Warm regards, Vapi Customer Support Team

Try updating your config to use JSON booleans (`true`/`false`) instead of Python (`True`/`False`), and explicitly set

voicemailDetectionType

for more reliable fallback. Here’s an example:

json
"transferPlan": {
  "mode": "warm-transfer-experimental",
  "holdAudioUrl": "https://file.mp3",
  "voicemailDetectionType": "transcript",
  "summaryPlan": {
    "enabled": true,
    "messages": [
      { "role": "system", "content": "Please provide a summary of the call." },
      { "role": "user", "content": "Here is the transcript:\n\n{{transcript}}\n\n" }
    ]
  },
  "fallbackPlan": {
    "message": "It seems the person is currently busy or on another call. Can I take a message?",
    "endCallEnabled": false
  }
}

Switching to JSON booleans and adding

voicemailDetectionType

should help the fallback trigger as expected ([documentation](https://docs.vapi.ai/call-forwarding)). Source: - [Call Forwarding Documentation](https://docs.vapi.ai/call-forwarding)