title: WP Rest API: new route return rest_invalid_handler
body: <p>This is a simple test script for create a new route:</p>
  
  <pre><code>add_action( 'rest_api_init', function () {
    register_rest_route( 'ass', '/ativar', array(
      'methods' =&gt; 'GET',
      'callback' =&gt; 'testing_route',
    ) );
  } );
  
  function testing_route($data){
      return array( 'message' =&gt; 'testing route' );
  }
  </code></pre>
  
  <p>But it returning an error message: </p>
  
  <blockquote>
    <p>rest_invalid_handler</p>
  </blockquote>