PayPal\Api\Details::setSubtotal PHP Method

    public function setSubtotal($subtotal)
    {
        NumericValidator::validate($subtotal, "Subtotal");
        $subtotal = FormatConverter::formatToPrice($subtotal);
        $this->subtotal = $subtotal;
        return $this;
    }

 public function postPayment($producto_id)
 {
     $producto = Producto::find($producto_id);
     if (is_null($producto)) {
         App::abort(404);
     }
     $productoYaComprado = User::find(Auth::user()->id)->Productos()->whereProducto_id($producto->id)->first();
     if (!is_null($productoYaComprado)) {
         App::abort(404);
     }
     \Session::put('producto_id', $producto_id);
     $payer = new Payer();
     $payer->setPaymentMethod('paypal');
     $items = array();
     $subtotal = 0;
     $currency = 'MXN';
     $item = new Item();
     $item->setName($producto->nombre)->setCurrency($currency)->setDescription($producto->nombre)->setQuantity(1)->setPrice($producto->precio);
     $items[] = $item;
     $subtotal += $producto->precio;
     $item_list = new ItemList();
     $item_list->setItems($items);
     $details = new Details();
     $details->setSubtotal($subtotal);
     //->setShipping(100);
     //$total = $subtotal + 100;
     $total = $subtotal;
     $amount = new Amount();
     $amount->setCurrency($currency)->setTotal($total)->setDetails($details);
     $transaction = new Transaction();
     $transaction->setAmount($amount)->setItemList($item_list)->setDescription('');
     $redirect_urls = new RedirectUrls();
     $redirect_urls->setReturnUrl(\URL::route('payment.status'))->setCancelUrl(\URL::route('payment.status'));
     $payment = new Payment();
     $payment->setIntent('Sale')->setPayer($payer)->setRedirectUrls($redirect_urls)->setTransactions(array($transaction));
     try {
         $payment->create($this->_api_context);
     } catch (\PayPal\Exception\PPConnectionException $ex) {
         if (\Config::get('app.debug')) {
             echo "Exception: " . $ex->getMessage() . PHP_EOL;
             $err_data = json_decode($ex->getData(), true);
             exit;
         } else {
             return \Redirect::route('home')->with('message', 'Algo salió mal, inténtalo de nuevo más tarde.');
         }
     }
     foreach ($payment->getLinks() as $link) {
         if ($link->getRel() == 'approval_url') {
             $redirect_url = $link->getHref();
             break;
         }
     }
     // add payment ID to session
     \Session::put('paypal_payment_id', $payment->getId());
     if (isset($redirect_url)) {
         // redirect to paypal
         return \Redirect::away($redirect_url);
     }
     return \Redirect::route('home')->with('message', 'Ups! Error desconocido. Inténtalo de nuevo más tarde.');
 }