Our assistant is configured with the DTMF tool to send keypad inputs (e.g., “1”) during outbound calls for navigating IVR menus. The assistant is using the GPT-4o model, and the tool is linked correctly via toolIds. During a live outbound call (not a sandbox or preview session), when the IVR prompts with “Press 1 to continue”, the assistant logs show that it successfully calls the DTMF tool with {"digits": 1} and the result is "Success.". However, the IVR does not react — it behaves as if no key was pressed.

Hi ismailaskarov, Based on the documentation and previous related issues, here are some steps to resolve the issue where the IVR doesn't respond despite successful DTMF tool calls: 1. **Verify DTMF Method**: Ensure you are using the out-of-band RFC 2833 method, which is more reliable for VoIP applications. This method is widely supported and should align with most IVR systems ([source](https://docs.vapi.ai/tools/default-tools)). 2. **Check Telephony Provider Compatibility**: Occasionally, IVR systems may not capture the DTMF signals properly due to telephony provider compatibility issues. Consider testing with a different telephony provider. 3. **Check IVR System Settings**: Ensure the IVR system is configured to accept DTMF inputs via the chosen method (RFC 2833). Configuration settings on the IVR or network level might need adjustment. 4. **Prompt Clarification**: Double-check the assistant's instructions to verify the prompt explicitly instructs the assistant to employ the DTMF tool for such actions ([here](https://docs.vapi.ai/assistants/function-calling)). 5. **Network Quality and Latency**: Network issues might lead to DTMF tones not being recognized. Check for any latency or quality issues on the call path. 6. **Call Logs Analysis**: Review the call logs for any potential logging of errors or issues that might have been overlooked. Ensure proper HTTP 200 responses are being received for the DTMF tool calls ([troubleshooting guide](https://docs.vapi.ai/tools/custom-tools-troubleshooting)). 7. **Testing with Different IVR**: If possible, perform tests with different IVRs to ensure it's not an issue specific to one system. If these steps do not help, consider reviewing call and IVR logs in-depth to identify the particular point of failure, or consult with your telephony provider for further network-related insights.

Hi Kyle Brunker, here is the screenshot of the call transcript: as you see, it shows the DTMF tool successfully, however nothing get pressed during the call. CALL ID: eef1c2bb-2173-4e84-a373-ce2f72a58601 https://cdn.discordapp.com/attachments/1397638544301756426/1398262100006010940/image.png?ex=6884b88f&is=6883670f&hm=32617147c31312a3f0dad982085877596e997ed823393a81abb38b0b5ace7a4d&

Depending on your telephony provider, you might need to test your assistant with a different telephony provider as some support sending DTMF tones in more compatible frequencies. We have heard from other customers that Twilio or Telnyx have pretty good support for sending DTMF. As for the VAPI tool side, the tool is successfully sending the digits. We recommend **Checking your Telnyx Console**: Verify in your Telnyx portal that DTMF relay is configured properly for your SIP trunk. The recommended setting is usually RFC2833.