Skipping form validation with a custom action button
To send a redirect response from a form use setRedirect() or setRedirectUrl():

  function cancel_submit(array &amp;$form, FormStateInterface $form_state) {
    $form_state-&gt;setRedirectUrl($url);
  }


And add '#limit_validation_errors' =&gt; array() to the cancel button as already mentioned in the question to prevent validation errors.