Page not found - Even after I implemented Hook_Menu()
With the code you posted you will get a blank page.

If you actually return something from your callback you will get a proper page, with no 404 error.
A menu callback has to actually return something.

For example, this works:



function user_type_registration_menu() {
  $items = array();

  $items['paypal/payment/ipn'] = array(
    'title' =&gt; t('Paypal Payment IPN'),
    'description' =&gt; t('Paypal Payment IPN'),
    'type' =&gt; MENU_CALLBACK,
    'page callback' =&gt; 'paypal_payment_paypal_ipn_callback',
    'access callback' =&gt; TRUE,
  );

  return $items;
}

function paypal_payment_paypal_ipn_callback() {
  dpm("here");
  return 'test';
}


Also, make sure your module is named "user_type_registration" or else your menu hook will not get picked up.