@Subscribe
 public void onPaymentSuccess(PaymentSuccess event) {
   paymentHandler.clearPayment();
   // TODO Handle success
 }
 @Subscribe
 public void onPaymentFailure(PaymentFailure event) {
   paymentHandler.clearPayment();
   // TODO Handle failure
 }
 @Override
 public void onBackPressed() {
   finish();
   paymentHandler.clearPayment();
   cart.clear();
 }