title: Woocommerce subscription hook argument only passing user id
body: <p>I'm tapping into the subscription action hook <code>scheduled_subscription_payment</code>. </p>
  
  <pre><code>function subscription_renewal($arg) {
      echo, '&lt;pre&gt;' print_r($arg, true);
  }
  add_action( 'scheduled_subscription_payment', 'subscription_renewal' );
  </code></pre>
  
  <p>Its only returning the user id of the subscriber and I've also tried multiple arguments. I want all the order (subscription) information but cannot find another method to do so. Does this method pass anything but the user id or is there another method?</p>