sad-indigoS
VAPI•3mo ago
sad-indigo

Voice Assistant Goes Silent After DTMF Input

Call ID: 0199b0ad-4982-7007-a7df-9a2c290d3956

Assistant ID: cd79ac7e-b3bb-49fd-8dc0-6556a3ba714e

I’m experiencing a recurring issue with my assistant that handles appointment bookings via phone. It uses a DTMF flow to let customers enter their phone number on the keypad.

Everything works perfectly in chat mode, but in voice calls, the behavior is inconsistent and often breaks after the DTMF stage.

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Setup Details:


  • Assistant purpose: Booking appointments to Google Calendar
  • Tools used:
    • check_availability
    • book_appointment
    • cancel_appointment
    • send_text_tool
    • Previously dtmf_tool (for phone number input)
  • Model: GPT-5
  • Voice provider: ElevenLabs
  • Transcriber: Deepgram
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Prompt (short version):

Collect and confirm date/time → then collect and confirm phone number → complete booking or cancellation → send SMS confirmation.


After digits are entered and tool completes, the assistant should confirm the number aloud and continue.


The call goes like this:

  • Assistant recognizes digits correctly.
  • When dtmf_tool completes, assistant is just silent. Then II need to speak, and it sometimes repeats the number confirmation endlessly in a loop.
  • If I add a tool.completed message, assistant most often just hangs up after confirming the number. But sometimes before entering the number (very unreliable)
What is happening?? It works perfectly in chat mode. This is very frustrating as I cant deliver my projects to my customers using Vapi.

I love Vapi, but this issue is killing me.

@Shubham Bajaj please take a look this.

Related issue: supportVoice Assistant goes silent during the call
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