Json数据如何获取PHP的内容

I am trying to use the paypal developer SDK for PHP for the first time. I have followed a tutorial on youtube all going well until I tried to execute it and the response I recieved was malformed_request JSON request doesn not map to API request. How do I get the struscture and contents of the JSON object so I can investigate further? please see code below error happens on the try. I am developing in netbeans 7.4

<?PHP
//this is copied from this tutorial here on youtube https://www.youtube.com/watch?v=BD1dOWIABe0
use PayPal\Api\Payer;
use PayPal\Api\Item;
use PayPal\Api\ItemList;
use PayPal\Api\Details;
use PayPal\Api\Amount;
use PayPal\Api\Transaction;
use PayPal\Api\RedirectUrls;
use PayPal\Api\Payment;
require '/../app/start.php';
$pTotal = 20.00;
$shipping = 1.00;
$Total = $pTotal + $shipping ;
$payer = new Payer();
$payer->setPaymentMethod('paypal');
$item = new Item();
$item->setName("tieThisToSomething")
->setCurrency('GBP')
->setQuantity(1)
->setPrice($pTotal);
$itemList = new ItemList();
$itemList->setItems($item); //I have removed square brackets from here []
$details = new Details();
$details->setShipping($shipping)
    ->setSubtotal($pTotal);
$amount = new Amount();
$amount->setCurrency('GBP')
    ->setTotal($Total)
    ->setDetails($details);
$transaction = new Transaction();
$transaction->setAmount($amount)
    ->setItemList($itemList)
    ->setDescription('Pay for all your santa fun')
    ->setInvoiceNumber(uniqid());//perhaps tie this to order number?

$redirectUrls = new RedirectUrls();
$redirectUrls->setCancelUrl(SITE_URL . '/pay.php?success=false')
         ->setReturnUrl(SITE_URL . '/pay.php?success=true'); 

$payment = new Payment();
$payment->setPayer($payer)
    ->setTransactions($transaction)
    ->setIntent('sale')
    ->setRedirectUrls($redirectUrls)   ; //should [] be needed here?

//try {
//    $payment->create($paypal);
//} catch (Exception $e) {
//    die($e);
//}

try {
   $payment->create($paypal);  //Error happens here!
} catch (PayPal\Exception\PayPalConnectionException $ex) {
  echo $ex->getCode(); // Prints the Error Code
  echo $ex->getData(); // Prints the detailed error message 
 die($ex);
} catch (Exception $ex) {
 die($ex);
}

$approvalUrl = $payment->getApprovalLink();
header("Location: {$approvalUrl}");

Adding logging would definitely help you investigate the raw details of the message. Here is the link to add configurations to enable logging:

https://github.com/paypal/PayPal-PHP-SDK/wiki/Adding-Configurations

Also, there are a lot of sample codes that could help you setup your code. Here is the one that shows creating "Payment with PayPal". You could infact run those locally by following instructions here.