No problem,
Did you first try to set a name in the field "stream name"? For example "test123".
Then if the connection is correct you should see the "test123" publication created in MonaServer logs :
Now if nothing happen it could mean that you are not on the same network when using LiveU. I don't know how LiveU works but if the rtmp connection comes from an external address (the public internet) you'll need to setup your router port forwarding to resolve your problem. This is needed if your RTMP client is on the public internet and your server is running on your local network.
Regards
Thomas