Getting separate ports to communicate in MEAN stack

I'm trying to set up a MEAN stack to integrate with Stripe. I would like to charge the card, and then save the Stripe token and user's email to a database. I'm currently running Angular on port 9000 and Express on port 3000. I'm having trouble getting my Angular form to post to the server. Nodemon is generating the following error:

app.set('port', port); TypeError: undefined is not a function

Any thoughts on what I'm doing wrong here?

HTML:

 <form stripe-form="handleStripe">
   <div class="form-group">
      <label>Card number</label>
      <input type="text" class="form-control" ng-model="number" payments-validate="card" payments-format="card" payments-type-model="type" ng-class="myForm.number.$card.type"/>
   </div>

   <div class="form-group">
    <label>Expiration</label>
   <input type="text" class="form-control" ng-model="expiry" payments-validate="expiry" payments-format="expiry" />
  </div>

  <div class="form-group">
    <label>CVC</label>
    <input type="text" class="form-control" ng-model="cvc" payments-validate="cvc" payments-format="cvc" payments-type-model="type"/>
 </div>
 <button type="submit" class="btn btn-primary btn-large">Submit</button>
</form>

Javascript for server

var router = express.Router();
var Customer = require('../app.js');
module.exports = router;
var express = require('express');
var path = require('path');
var bodyParser = require('body-parser');
var mongoose = require('mongoose');
var cors = require('cors');
var routes = require('./routes/index');
mongoose.connect('mongodb://localhost/test');

var customerSchema = {
 token:String,
 email: String
}

var Customer = mongoose.model('Customer', customerSchema, 'customers')

var app = express();
app.use(cors());

app.post('/customers', function (req, res) {
  Customer.find(function (err, doc) {
   res.send(doc);
 })
})

app.listen(3000);

var stripe = require("stripe")("sk_test_KEY");

stripe.charges.create({
  amount: 400,
  currency: "usd",
  source: "tok_15dKVmKUwBWfcUd6tTMAdnXN", 
  description: "Charge for test@example.com"
  }, function(err, charge) {   
  });

   //from the bin folder:
   var port = normalizePort(process.env.PORT || '3000');
   app.set('port', port);

Javascript on client side:

.controller('MainCtrl', function ($scope) {
$scope.handleStripe = function(status, response){
  if(response.error) {

  } else {

    token = response.id;
}
};
});

[EDIT: Added javascript for client side and info related to app.set('port', port);]