node.js express app 404 in Facebook's iframe

Have setup a basic application on node.js & been trying to run it on Facebook apps platform since over 12 hours now but nothing works.

I can successfully access the application using original domain i.e., https://codebook.vaibhavpandey.com but whenever I try to access it via Facebook Apps using https://apps.facebook.com/vpz_codebook/, express renders the 404 view.

This is my main.js if you want to have a look at. My first day on node.js & Facebook Apps so don't be rude please :P

var express = require('express');
var path = require('path');
var favicon = require('static-favicon');
var logger = require('morgan');
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');

var index = require('./routes/index');

var app = express();

app.locals.name = 'Codebook';

app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'jade');

app.use(favicon());
app.use(bodyParser.json());
app.use(bodyParser.urlencoded());
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));
app.use(logger('combined'));

app.use('/', index);

app.use(function(req, res, next) {
    console.log(req);
    var err = new Error('Oops! No code here...');
    err.status = 404;
    next(err);
});

app.use(function(err, req, res, next) {
    res.status(err.status || 500);
    res.render('error', {
        title: err.message,
        uri: (req.protocol + '://' + req.get('host') + req.originalUrl)
    });
});


module.exports = app;

This is the routes/index.js file, containing the only route:

var express = require('express');
var router = express.Router();

router.get('/', function(req, res) {
  res.render('index');
});

module.exports = router;