/**
  * Add action when the payment page is complete and before the review page. 
  * @param  SI_Checkouts $checkout 
  * @return                  
  */
 public function processed_payment_page(SI_Checkouts $checkout)
 {
     if ($checkout->is_page_complete(SI_Checkouts::PAYMENT_PAGE)) {
         // Make sure to send offsite when it's okay to do so.
         do_action('si_send_offsite_for_payment', $checkout);
     }
 }