Laravel 5 PayPal错误400

Question

我有：

public function store(Request $request)
    {

        $name_chunks = explode(' ', $request->get('name'));
        $expire_chunks =explode(' / ', $request->get('expiry'));

        $number = str_replace(' ', '', $request->get('number'));

        $inn = (int) mb_substr($number, 0, 2);

        if ($inn >= 40 && $inn <= 49) {
            $type = 'visa';
        } else if ($inn >= 51 && $inn <= 55) {
            $type = 'mastercard';
        } else if ($inn >= 60 && $inn <= 65) {
            $type = 'discover';
        } else if ($inn >= 34 && $inn <= 37) {
            $type = 'amex';
        } else {
            throw new \UnexpectedValueException('Unsupported card type.');
        }

        // ### CreditCard
        $card = Paypalpayment::creditCard();
        $card->setType($type)
            ->setNumber($number)
            ->setExpireMonth($expire_chunks[0])
            ->setExpireYear($expire_chunks[1])
            ->setCvv2($request->get('cvc'))
            ->setFirstName($name_chunks[0])
            ->setLastName($name_chunks[1]);

        // ### FundingInstrument
        // A resource representing a Payer's funding instrument.
        // Use a Payer ID (A unique identifier of the payer generated
        // and provided by the facilitator. This is required when
        // creating or using a tokenized funding instrument)
        // and the `CreditCardDetails`
        $fi = Paypalpayment::fundingInstrument();
        $fi->setCreditCard($card);

        // ### Payer
        // A resource representing a Payer that funds a payment
        // Use the List of `FundingInstrument` and the Payment Method
        // as 'credit_card'
        $payer = Paypalpayment::payer();
        $payer->setPaymentMethod("credit_card")
            ->setFundingInstruments(array($fi));

        $item1 = Paypalpayment::item();
        $item1->setName('Ground Coffee 40 oz')
            ->setDescription('Ground Coffee 40 oz')
            ->setCurrency('USD')
            ->setQuantity(1)
            ->setTax(0.3)
            ->setPrice(7.50);

        $item2 = Paypalpayment::item();
        $item2->setName('Granola bars')
            ->setDescription('Granola Bars with Peanuts')
            ->setCurrency('USD')
            ->setQuantity(5)
            ->setTax(0.2)
            ->setPrice(2);


        $itemList = Paypalpayment::itemList();
        $itemList->setItems(array($item1, $item2));


        $details = Paypalpayment::details();
        $details->setShipping("1.2")
            ->setTax("1.3")
            //total of items prices
            ->setSubtotal("17.5");

        //Payment Amount
        $amount = Paypalpayment::amount();
        $amount->setCurrency("USD")
            // the total is $17.8 = (16 + 0.6) * 1 ( of quantity) + 1.2 ( of Shipping).
            ->setTotal("20")
            ->setDetails($details);

        // ### Transaction
        // A transaction defines the contract of a
        // payment - what is the payment for and who
        // is fulfilling it. Transaction is created with
        // a `Payee` and `Amount` types

        $transaction = Paypalpayment::transaction();
        $transaction->setAmount($amount)
            ->setItemList($itemList)
            ->setDescription("Payment description")
            ->setInvoiceNumber(uniqid());

        // ### Payment
        // A Payment Resource; create one using
        // the above types and intent as 'sale'

        $payment = Paypalpayment::payment();

        $payment->setIntent("sale")
            ->setPayer($payer)
            ->setTransactions(array($transaction));

        try {
            // ### Create Payment
            // Create a payment by posting to the APIService
            // using a valid ApiContext
            // The return object contains the status;
            $payment->create($this->_apiContext);
        } catch (\PPConnectionException $ex) {
            return "Exception: " . $ex->getMessage() . PHP_EOL;
            exit(1);
        }

        return redirect('/booking/thanks');
    }

但我得到了：

PayPalConnectionException in PayPalHttpConnection.php line 176:
Got Http response code 400 when accessing https://api.sandbox.paypal.com/v1/payments/payment.

任何想法我做错了什么？