I created this drawing early in v2.0's birth process, it's a tiny bit out of date...
The config.json is describing this picture to HubConnect NodeJS Server. The NodeJS Server knows it's own IP, so that's not in config.json. But it needs the IP address of every hub that will be sending it messages. You have to also assign a name, and that will show in the NodeJS logs. Feel free to use anything reasonable.. Disney Princesses if you'd like
For each hub that will be communicating with HubConnect NodeJS Server gets a 'block' in that config.json. The IP of the Hub, a name that appears in the logs and most importantly, a PORT number that is unique and unused on the Computer that is hosting your NodeJS. Our samples all use 22000 - 22010 but you can anything that meets the criteria.
If you use my tool for building this config.json, it begins with the Hub running HubConnect Server for Hubitat definition then any/all of the connected Hubitat Hubs.
As to filling in the config inside HubConnect Server Instance for each connection pair, you must identify the IP address of your HubConnect NodeJS Server and the port you've assigned to THIS Hub.. the one you're entering values in/on. Since this is the Server Instance app, then you must also identify the port you assigned to that hub in the config.json.
So.. let's use the drawing and follow a flow...
The top Hub, let's pretend that's the Hubitat Hub running HubConnect Server for Hubitat and has a Server Instance being edited. It wants the IP address of HubConnect NodeJS Server and (following the Yellow Arrow down...) the PORT that HubConnect NodeJS Server is Listening on for that Hub, as defined in config.json.
The Events flowing out of the Server Hub, enter the listener on HubConnect NodeJS Server and then sent via a Websocket to the connected Hub. (Following a Blue Arrow down..) The connected Hub will respond (Yellow Arrow upwards) to the PORT that HubConnect NodeJS Server is Listening on for that Hub, as defined in config.json. The Event will flow out of HubConnect NodeJS Server (following the Blue Arrow upwards) back into the Server Hub, thus completing the loop.
the * is Hubitat standard for a required field.
Too much detail I'm afraid, but I just don't know where your perception is going sideways I really hope that somewhere in this message is the "ahhha" hint.