Symfony2 payum paypal express简单结账

我是Payum的新手。很多事情都把我搞糊涂了。我试图建立一个简单的贝宝快递结帐就像例子显示在Payum文件。然而，当我试图处理付款时，它显示了一个异常:

" my_paypal_express_checkout不存在。500服务器内部错误- InvalidArgumentException"

配置如下:

payum:
security:
    token_storage:
        Acme'PaymentBundle'Entity'PayumSecurityToken:
            doctrine:
                driver: orm
storages:
    Acme'PaymentBundle'Entity'PaymentDetails:
        doctrine: 
            driver: orm
contexts:
    Ibase_paypal_express:
        paypal_express_checkout_nvp:
         ...codes...

下面是控制器中prepare和done动作的代码:

public function preparePaypalAction(Request $request)
{
    $paymentName = 'ibase_paypal_express_checkout';
    $form = $this->createPurchaseForm();
    $form->handleRequest($request);
    if ($form->isValid()) {
        $data = $form->getData();
        $storage = $this->get('payum')->getStorage('Ibase'PaymentBundle'Entity'PaymentDetails');
        /** @var 'Ibase'CartBundle'Entity'PaymentDetails $paymentDetails */
        $paymentDetails = $storage->createModel();
        $paymentDetails['PAYMENTREQUEST_0_CURRENCYCODE'] = $data['currency'];
        $paymentDetails['PAYMENTREQUEST_0_AMT'] = $data['amount'];//total amount ??
        $storage->updateModel($paymentDetails);
        $captureToken = $this->get('payum.security.token_factory')->createCaptureToken(
            $paymentName,
            $paymentDetails,
            'payment_done' // the route to redirect after capture;
        );
        $paymentDetails['INVNUM'] = $paymentDetails->getId();
        $paymentDetails['RETURNURL'] = $captureToken->getTargetUrl();
        $paymentDetails['CANCELURL'] = $captureToken->getTargetUrl();
        $storage->updateModel($paymentDetails);
        return $this->redirect($captureToken->getTargetUrl());
    }
    return $this->render('PaymentBundle:PaypalExpress:paypalPrepare.html.twig', array(
        'form' => $form->createView(),
        'paymentName' => $paymentName
    ));
}
public function doneAction(Request $request)
{
    $token = $this->get('payum.security.http_request_verifier')->verify($request);
    $payment = $this->get('payum')->getPayment($token->getPaymentName());
    $status = new BinaryMaskStatusRequest($token);
    $payment->execute($status);
    if ($status->isSuccess()) {
        $this->getUser()->addCredits(100);
        $this->get('session')->getFlashBag()->set(
            'notice',
            'Payment success. Credits were added'
        );
    } else if ($status->isPending()) {
        $this->get('session')->getFlashBag()->set(
            'notice',
            'Payment is still pending. Credits were not added'
        );
    } else {
        $this->get('session')->getFlashBag()->set('error', 'Payment failed');
    }
    return $this->redirect('home');
}
 /**
 * @return 'Symfony'Component'Form'Form
 */
protected function createPurchaseForm()
{
    return $this->createFormBuilder()
        ->add('amount', null, array(
            'data' => 1,
            'constraints' => array(new Range(array('max' => 2)))
        ))
        ->add('currency', null, array('data' => 'AUD'))
        ->getForm()
    ;
}

任何人都可以帮助将不胜感激!