Drupal 8 Form Alter to redirect User from User Registration Form

Drupal8FormAlter.php

<?php

/**
 * Implements hook_form_FORM_ID_alter().
 */
function mymodule_form_user_register_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  // @todo come up with a more elegant approach here.
  // Alter login form and add own custom submit handler.
  $form['actions']['submit']['#submit'][] = '_mymodule_user_register_form_submit';
}

/**
 * Custom submit handler for registration form.
 */
function _mymodule_user_register_form_submit($form, FormStateInterface $form_state) {
  // Set redirect to login form.
  $url = Url::fromUri('internal:/form/registration');
  $form_state->setRedirectUrl($url);
}

I tried it but give me an error. This is my code if i am doing something wrong please help me out.
`function shortlist_custom_submit(array $form, FormStateInterface &$form_state) {

$url = Url::fromUri('internal:/node/4');
$form_state->setRedirectUrl($url);

}`