Description:
We’re seeing outbound calls from our 3CX system being canceled immediately after receiving “180 Ringing” from Twilio. Twilio accepts authentication and begins ringing the destination number, but 3CX sends a SIP CANCEL with Reason: SIP;cause=200;text="Call terminated".The call never completes — it starts to ring and then drops within a few seconds.
The calls do not cancel and complete successfully when the activity log level is set to verbose...
I've had the Twilio as a backup trunk for several years and normally we do not notice if the main trunk fails, other than the caller ID shows as a Twilio number. Our main trunk is down this morning due to provider fiber issues.
Environment:
- 3CX Version: 20.0.7.1060
- Trunk Provider: Twilio (PSTN trunk)
- Transport: UDP
SIP Trace Summary:
- 3CX sends initial INVITE → Twilio responds 407 Proxy Authentication Required.
- 3CX resends INVITE with authentication → Twilio responds with:
- 100 Trying
- 183 Session Progress
- 180 Ringing
- Before any 200 OK is received, 3CX sends CANCEL:
Code:CANCEL sip:[email protected]:5060 SIP/2.0 Reason: SIP;cause=200;text="Call terminated"
- Twilio responds:
Code:CANCEL sip:[email protected]:5060 SIP/2.0 Reason: SIP;cause=200;text="Call terminated"
The Twilio logs confirm they did not reject the call — it was actively ringing when 3CX canceled.
Questions:
Why is 3CX sending the CANCEL after the call has already started ringing?
Are there internal timeout or routing conditions that would trigger this?
Where should I check in logs or configuration to determine the root cause?
Why does changing the log level allow the call to complete?
