socket.io connection doesn't work, xhr poll error

I tried cloning the chat example in socket.io tutorial and it just wouldn't work. Then I installed firecamp and found out that socket.io is at fault.
I typed socket.firecamp.io in the address bar and I got the following error:
Error: xrh poll error
How can I fix it?
Here's the code:

//Connection
const socket = io( "socket.firecamp.io", {
  "transports": ["polling","websocket"]
});

socket.on("disconnect", () => {
  console.log("socket disconnected");
});

// for more information: https://github.com/socketio/socket.io-client/blob/master/docs/API.md