Hey, thanks a lot for the insight — really helpful. In my case, I’m not running LiveKit or any custom media server. The setup is direct SIP trunking from Telnyx to Retell, so there’s no infrastructure on my side that could be causing NAT/firewall issues. What I’m seeing is: SIP signaling completes successfully (INVITE → 200 OK → ACK) On Retell recordings, I can hear the AI audio correctly The callee reports they don’t hear anything at all (not even the AI) I also don’t receive any inbound audio from the callee In some cases, Telnyx even shows the call duration as 0 seconds So effectively it’s a no-audio / one-way audio issue, but with no custom media server in between. Because of that, I’m thinking it might be: RTP not being properly routed between Telnyx and Retell SDP mismatch (wrong IP/port advertised) Codec negotiation issue Does that still sound like a NAT-type issue to you, or more like a provider-to-provider media negotiation problem? I’m already sharing PCAPs with Telnyx, but if you have any specific things you’d check in the SDP (or Wireshark) to confirm this, that would help a lot.