The server needs to open the level in listen mode, this is accomplished by adding “?listen” to the end of the map name. Something like TravelToMap node with “MyMapName?listen”. Don’t have the editor here, so unfortunately I can’t give you any screenshots right now.
For local testing, I recommend you test it with multiple “real” instances, and not with instances out of the editor, as the editor automatically start the map in listen mode, when you select to launch multiple instances.
For starting multiple “real” instances, simply right-click on your .uproject file and select “Launch Game”. You can do this mutliple times, and each will launch a “real” instance. See if you can connect the instances together. If this works, it will also work via internet, provided you have the correct ip/port and port forwarding settings (and maybe check firewall for good measure).
Cheers, Elewyth