code: public static function checkout($cart = null)
      {
          $success = true;
          try {
              if (empty(static::$gatewayKey)) {
                  throw new ShopException('Payment gateway not selected.');
              }
              if (empty($cart)) $cart = Auth::user()->cart;
              static::$gateway->onCheckout($cart);
          } catch (ShopException $e) {
              static::setException($e);
              $success = false;
          } catch (CheckoutException $e) {
              static::$exception = $e;
              $success = false;
          } catch (GatewayException $e) {
              static::$exception = $e;
              $success = false;
          }
          if ($cart)
              \event(new CartCheckout($cart->id, $success));
          return $success;
      }
docs: Checkout current user's cart.
  
  @param object $cart For specific cart.
  
  @return bool