Help needed with ajax request from Jquery to callback function

Question

I create the callback url 'swish_payment/request' in my hook_menu() function:

function swish_payments_menu(){
  $items['swish_payment/request'] = array(
    'type'             => MENU_CALLBACK,
    'page callback'    => '_ajax_payment_request',
    'access callback' => TRUE,
    'file' => 'src/controller/CallbackController.inc',
  );
  return $items;
}

In the file CallbackController.inc, saved in the folder 'src/controller' stated after "file" above I have this:

function _ajax_payment_request() {

  drupal_json_output('It works!');

}

..just to check that the callback works. And this is how the js looks like in the client ('number' contains a string):

$.ajax({
  data:number,
  dataType: "json",
  type:"POST",
  url : "swish_payment/request",
  cache: false,
  success: function (response) {
    console.log(response);
  }
});

Under the networks tab i Chrome I can see that the url 'swish_payment/request' is found with a 200 code. But the console stays blank.

Can anyone give me a hint on what I am doing wrong?

EDITED: turns out that it worked when I moved the function from the external file into the .module file. Apparently it's a bad idea to split code into several files.