Peerjs-on-node - Cannot connect sender & receiver

I am trying to implement some very simple UDP communication between two clients (Server.js and Index.js), both using Peer.js (Peerjs-on-Node) and Node.js.

Index.js is as follows:

const Peer = require('peerjs-on-node').Peer;

var peer = new Peer("c48ce5c1-364b-4e82-aa5c-19fe05f6a61f");
const conn = peer.connect("02addcc4-bba1-46e4-8ed6-a210e179f732");
conn.on("open", () => {
    conn.send("Hi!");
});

while Server.js is:

const Peer = require('peerjs-on-node').Peer;

var peer = new Peer("02addcc4-bba1-46e4-8ed6-a210e179f732");
peer.on("connection", (conn) => {
    conn.on("data", (data) => {
        console.log(data);
    });
});

The peer id's are static (randomly generated for this example).

I get no obvious errors when running the above, but also no expected output.

Can anyone diagnose? I thought I'd stripped this back to the simplest variation I could but still no success.