Troubleshooting bi-directional audio issues with callin.io and Twilio

Hello everyone

I’ve developed an outbound voice call agent utilizing callin.io + Twilio + Ultravox. Here’s a breakdown of its operation:

• Phone numbers are retrieved from Google Sheets.
• A call is initiated to the number using Twilio’s API, employing a TwiML that links to the Ultravox WebSocket URL.
• Prior to this, a POST request is sent to Ultravox’s /api/calls endpoint to obtain the joinUrl.

• The process appears to be functioning correctly in several aspects:

  • The call successfully reaches the recipient.
  • Ultravox recognizes the connection and logs the conversation attempt.
  • The system prompt and the initial message are visible in the Ultravox logs.

HOWEVER — during the actual phone call:

• I cannot hear anything from Ultravox.
• Ultravox also fails to receive my speech (no response or logs are generated based on my input).

Essentially, the call connects, but bi-directional audio is entirely non-functional.

I’ve performed the following checks:

• Audio sample rates are confirmed at 8000 Hz (as expected for Twilio).
• The WebSocket configuration in Ultravox’s payload seems correct.
• The Twilio call is correctly hitting the TwiML with the stream.

Screenshots from Ultravox are attached, illustrating that it detects the call and the initial message transmission.

Any insights would be greatly appreciated — could this be related to Twilio’s stream setup, how callin.io is handling it, or the Ultravox configuration?

Thanks in advance