**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. --- ### 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 --- 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: https://discord.com/channels/1211482211119796234/1377398718847910000

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

After sending DTMF input, ensure your assistant replies with a single space character (

" "

) to stay silent and avoid overlapping or premature speech. This helps prevent the assistant from hanging or looping after DTMF entry in voice calls.

json
{
  "reply": " "
}

Try adding this silent reply immediately after the DTMF tool completes, before prompting for confirmation. This approach is recommended for reliable IVR/DTMF flows in Vapi voice calls according to the documentation. Source: - [IVR Navigation Guide](https://docs.vapi.ai/ivr-navigation)

That did absolutly nothing, like I expected.

Hi Preben, To effectively navigate IVR menu systems using Vapi, consider these recommendations: 1. Add Short Pauses: Use pause characters like

w

for a 0.5s pause and

W

for a 1s pause between digits. Example:

1w2w3W4#

for Twilio, Telnyx, Vapi Numbers, and BYOK SIP. 2. Wait for Menus to Finish: Ensure your assistant waits until all options are spoken before sending DTMF sequences. Use a single space character (" ") to remain silent during these pauses. 3. Retry with Slower Inputs: If initial attempts fail, try sending digits more slowly. Start with fast (

123#

), then medium (

1w2w3#

with 0.5s gaps), and slow (

1W2W3#

with 1s gaps) retries. If required, use spoken input as a fallback. For detailed guidance, please refer to the [IVR Navigation documentation](https://docs.vapi.ai/ivr-navigation). If there are any more specific issues or configurations you need assistance with, feel free to ask.

where does this go? "1W2W3#" for example? or is it generated by something? and where? I'm totalyl clueless about what you're referring to. is it a owrkflow or is it the standard setup with jsut a system prompt that has thiss? or is this a tool call? explain

Let me explain this IVR (Interactive Voice Response) navigation guidance : 1. Pause Characters: - When entering numbers (like menu selections or account numbers), you should add pauses between digits -

w

= 0.5 second pause -

W

= 1 second pause - Example: To enter "1234#" with pauses, write it as

1w2w3W4#

- This helps ensure the IVR system registers each digit correctly 2. Waiting for Menu Options: - Let the IVR finish speaking all options before responding - Use a single space " " as your assistant's response to stay silent - This prevents the assistant from talking over the IVR menu 3. Progressive Retry Strategy: If the IVR doesn't recognize the input, try these approaches in order:

First try:  123#         (no pauses)Second try: 1w2w3#       (0.5s pauses)Third try:  1W2W3#       (1s pauses)Last resort: Speak the option out loud

This approach helps ensure reliable navigation through phone menu systems by adapting to different IVR timing requirements.

Has nothing to do with that, no.

Sorry about that, and thank you for letting me know. I appreciate the clarification