Woocommerce – Add order note via API callback

Building an integration with a 3rd party API which is posting to the URL http://www.mysite.com/subfolderinstall/wc-api/update_order/
Have the below code which isn’t working but I think demonstrates what I’m attempting to do. Wondering if the subfolder install is having an effect? May well just be poorly formed code. The order has the custom field external_order_id which is being added fine.
Any pointers gratefully received!

add_action( 'woocommerce_api_update_order', 'update_order_handler' );

function pwinty_update_order_handler() {
      $externalOrderId = $_POST["orderId"];
	  $event_status = $_POST["eventData"];
	  $args = array(
	  'numberposts' => 1,
	  'meta_key' => 'external_order_id',
	  'meta_value' => $externalOrderId
                      );
      $query = new WP_Query( $args );
	  if( $query->have_posts() ):  while ( $query->have_posts() ) : $query->the_post();
	  $wooOrderId = get_the_ID();
	  $order = new WC_Order($wooOrderId);
          $order->add_order_note($event_status);
	  endwhile;
	  endif;
	  wp_reset_query();

}