LetsEncrypted Node.js HTTPS Server inaccessible from browser. Why it won't load?

I secured NGINX with SSL following this tutorial: https://www.digitalocean.com/community/tutorials/how-to-secure-nginx-with-let-s-encrypt-on-ubuntu-16-04

I explicitly chose to redirect all requests to HTTPS.

Now, when visiting my webpage www.example.com, it correctly redirects me to https://www.example.com and shows the default NGINX text.

I want Express to run there, so I made this tiny script to test things out:

var https = require('https');
var fs = require('fs');

var options = {
  key: fs.readFileSync('/etc/letsencrypt/live/example.com/privkey.pem'),
  cert: fs.readFileSync('/etc/letsencrypt/live/example.com/cert.pem'),
  ca: fs.readFileSync('/etc/letsencrypt/live/example.com/chain.pem')
};

https.createServer(options, function (req, res) {
  res.writeHead(200);
  res.end("hello world\n");
}).listen(8000);

The page will not load at all. What am I doing wrong?