https://webrtc.github.io/samples/src/content/peerconnection/trickle-ice/

Click Acquire microphone/camera permissions checkbox, then click Gather candidates at bottom.  You need to see a line where the Type is "srflx".  If you don't, its blocked.  Then you can try changing the port to 3478 (CAREpoint 3 OP/Remote Monitor will try both 19302 and 3478).

Try changing port to 3478 if default 19302 does not return an "srflx" type.  To do this, double click the "stun:stun.l.google.com:19302" in the ICE Servers section, then modify the STUN or TURN URI to say "stun:stun.l.google.com:3478", then click Add Server.  Don't forget to remove the 19302 server.