When I am starting an outbound call I receive the following error code:`An error occurred in this call: call.in-progress.error-sip-outbound-call-failed-to-connect`. I am using Telnyx. Inbound calls are working.

To resolve the outbound call error, ensure you've set up outbound authentication for your Telnyx SIP trunk in Vapi. Use the following cURL command to create the required SIP trunk credential (replace the placeholders with your actual credentials):

bash
curl -X POST https://api.vapi.ai/credential \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_VAPI_PRIVATE_KEY" \
  -d '{
    "provider": "byo-sip-trunk",
    "name": "Telnyx Trunk",
    "gateways": [
      { "ip": "sip.telnyx.com", "inboundEnabled": false }
    ],
    "outboundAuthenticationPlan": {
      "authUsername": "YOUR_SIP_USERNAME",
      "authPassword": "YOUR_SIP_PASSWORD",
      "sipRegisterPlan": { "realm": "sip.telnyx.com" }
    }
  }'

This step is essential for enabling outbound calls through Telnyx. For more details, see the [Telnyx SIP integration guide](https://docs.vapi.ai/advanced/sip/telnyx). Source: - [Telnyx SIP integration](https://docs.vapi.ai/advanced/sip/telnyx)