The error "transaction failed to complete (0 intermediate responses)" indicates that SIP INVITE requests are being sent but no responses are received from the destination. Since this issue occurs even when calling LiveKit's echo server, it suggests a potential network or configuration issue. Here are some steps to troubleshoot and resolve this: 1. Verify Network Connectivity: ◦ Ensure that your LiveKit SIP service can reach the SIP provider's address (e.g., `echo.sip.livekit.io:5060`). ◦ Check for any firewall rules that might be blocking SIP traffic (typically UDP/TCP port 5060 or 5061 for TLS). ◦ If your setup is behind NAT, ensure proper NAT traversal configuration. 1. Check Transport Protocol: ◦ Verify that the transport protocol (UDP/TCP/TLS) matches what the SIP provider or destination expects. 1. DNS Resolution: ◦ Ensure that the SIP trunk address resolves correctly to the intended IP address. ◦ Check your DNS configuration if using custom DNS servers. 1. Monitor SIP Traffic: ◦ Use packet capture tools to confirm that SIP packets are being sent and check if any responses are received. 1. Validate Configuration: ◦ Double-check your SIP trunk configuration, including the address, credentials, and phone number format. Since the issue affects all outbound calls, including to LiveKit's echo server, the problem is likely related to network connectivity or transport protocol mismatches. Please review these areas and let me know if further assistance is needed. Sources: test/lktest-sip-outbound/README.md | Making outbound calls | LiveKit Docs | livekit/livekit_sip.pb.go