eBay Trading API additem call returns nothing, getting 'Undefined variable: response' error when loading page – Ebay API

I am trying to use addItem call to add a listing. Currently trying with sandbox credential received from eBay.

I am using this tutorial to do this: https://github.com/cahudson/eBayCommerceCookbook/blob/master/1_3_presenting_products_through_ebay/addItem.php

I have received key values correctly and set parameters also appropriately. When I load the page it gives this error:

Notice: Undefined variable: response in F:wampwwwebaytest1addItem.php on line 180

When I click on the addItem button, it does not show any error but no success message too. Any help would be very appreciable.

Entire code is here: https://gist.github.com/karimkhanp/16631ab90eb502131f9c

<?php
/********************************************
addItem.php

Uses eBay Trading API to list an item under 
a seller's account.

********************************************/

// include our Trading API constants
require_once 'tradingConstants.php';

// check if posted
if (!empty($_POST)) {

    // grab our posted keywords and call helper function
    // TODO: check if need urlencode
    $title = $_POST['title'];
    $categoryID = $_POST['categoryID'];
    $startPrice = $_POST['startPrice'];
    $pictureURL = $_POST['pictureURL'];
    $description = $_POST['description'];

    // call the getAddItem function to make AddItem call
  $response = getAddItem($title, $categoryID, $startPrice, $pictureURL, $description);

}

// Function to call the Trading API AddItem
function getAddItem($addTitle, $addCatID, $addSPrice, $addPicture, $addDesc) {

    /* Sample XML Request Block for minimum AddItem request
    see ... for sample XML block given length*/

    // Create unique id for adding item to prevent duplicate adds
    $uuid = md5(uniqid());

    // create the XML request
    $xmlRequest  = "<?xml version="1.0" encoding="utf-8"?>";
    $xmlRequest .= "<AddItemRequest xmlns="urn:ebay:apis:eBLBaseComponents">";
    $xmlRequest .= "<ErrorLanguage>en_US</ErrorLanguage>";
  $xmlRequest .= "<WarningLevel>High</WarningLevel>";
  $xmlRequest .= "<Item>";
  $xmlRequest .= "<Title>" . $addTitle . "</Title>";
  $xmlRequest .= "<Description>" . $addDesc . "</Description>";
  $xmlRequest .= "<PrimaryCategory>";
  $xmlRequest .= "<CategoryID>" . $addCatID . "</CategoryID>";
  $xmlRequest .= "</PrimaryCategory>";
  $xmlRequest .= "<StartPrice>" . $addSPrice . "</StartPrice>";
  $xmlRequest .= "<ConditionID>1000</ConditionID>";
  $xmlRequest .= "<CategoryMappingAllowed>true</CategoryMappingAllowed>";
  $xmlRequest .= "<Country>India</Country>";
  $xmlRequest .= "<Currency>USD</Currency>";
  $xmlRequest .= "<DispatchTimeMax>3</DispatchTimeMax>";
  $xmlRequest .= "<ListingDuration>Days_7</ListingDuration>";
  $xmlRequest .= "<ListingType>FixedPriceItem</ListingType>";
  $xmlRequest .= "<PaymentMethods>PayPal</PaymentMethods>";
  $xmlRequest .= "<PayPalEmailAddress>[email protected]</PayPalEmailAddress>";
  $xmlRequest .= "<PictureDetails>";
  $xmlRequest .= "<PictureURL>" . $addPicture . "</PictureURL>";
  $xmlRequest .= "</PictureDetails>";
  $xmlRequest .= "<PostalCode>380055</PostalCode>";
  $xmlRequest .= "<Quantity>1</Quantity>";
  $xmlRequest .= "<ReturnPolicy>";
  $xmlRequest .= "<ReturnsAcceptedOption>ReturnsAccepted</ReturnsAcceptedOption>";
  $xmlRequest .= "<RefundOption>MoneyBack</RefundOption>";
  $xmlRequest .= "<ReturnsWithinOption>Days_30</ReturnsWithinOption>";
  $xmlRequest .= "<Description>" . $addDesc . "</Description>";
  $xmlRequest .= "<ShippingCostPaidByOption>Buyer</ShippingCostPaidByOption>";
  $xmlRequest .= "</ReturnPolicy>";
  $xmlRequest .= "<ShippingDetails>";
  $xmlRequest .= "<ShippingType>Flat</ShippingType>";
  $xmlRequest .= "<ShippingServiceOptions>";
    $xmlRequest .= "<ShippingServicePriority>1</ShippingServicePriority>";
  $xmlRequest .= "<ShippingService>USPSMedia</ShippingService>";
  $xmlRequest .= "<ShippingServiceCost>2.50</ShippingServiceCost>";
  $xmlRequest .= "</ShippingServiceOptions>";
  $xmlRequest .= "</ShippingDetails>";
  $xmlRequest .= "<Site>India</Site>";
  $xmlRequest .= "<UUID>" . $uuid . "</UUID>";
  $xmlRequest .= "</Item>";
  $xmlRequest .= "<RequesterCredentials>";
  $xmlRequest .= "<eBayAuthToken>" . AUTH_TOKEN . "</eBayAuthToken>";
  $xmlRequest .= "</RequesterCredentials>";
  $xmlRequest .= "<WarningLevel>High</WarningLevel>";
    $xmlRequest .= "</AddItemRequest>";

    // define our header array for the Trading API call
    // notice different headers from shopping API and SITE_ID changes to SITEID
    $headers = array(
        'X-EBAY-API-SITEID:'.SITEID,
        'X-EBAY-API-CALL-NAME:AddItem',
        //'X-EBAY-API-REQUEST-ENCODING:XML',
        'X-EBAY-API-COMPATIBILITY-LEVEL:' . API_COMPATIBILITY_LEVEL,
        'X-EBAY-API-DEV-NAME:' . API_DEV_NAME,
        'X-EBAY-API-APP-NAME:' . API_APP_NAME,
        'X-EBAY-API-CERT-NAME:' . API_CERT_NAME,
        'Content-Type: text/xml;charset=utf-8'
    );

    // initialize our curl session
    $session  = curl_init(API_URL);

    // set our curl options with the XML request
    curl_setopt($session, CURLOPT_HTTPHEADER, $headers);
    curl_setopt($session, CURLOPT_POST, true);
    curl_setopt($session, CURLOPT_POSTFIELDS, $xmlRequest);
    curl_setopt($session, CURLOPT_RETURNTRANSFER, true);

    // execute the curl request
    $responseXML = curl_exec($session);

    // close the curl session
    curl_close($session);

    // return the response XML
    return $responseXML;
}
?>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8" />
<title>2-4 Add Item to eBay using eBay Trading API</title>
<style>
body {background: #fff; color: #000; font: normal 62.5%/1.5 tahoma, verdana, sans-serif;}
* {margin: 0; padding: 0;}
form {padding: 0 10px; width: 700px;}
legend {font-size: 2em; padding-left:5px;padding-right:5px; position: relative;}
fieldset {border: 1px solid #ccc; border-radius: 5px; padding: 10px; width: 320px;}
li {clear: both; list-style-type: none; margin: 0 0 10px;}
label, input {font-size: 1.3em;}
label {display: block; padding: 0 0 5px; width: 200px}
input {background-position: 295px 5px; background-repeat: no-repeat; border: 2px solid #ccc; border-radius: 5px; padding: 5px 25px 5px 5px; width: 285px;}
input:focus {outline: none;}
input:invalid:required {background-image: url(asterisk.png); box-shadow: none;}
input:focus:invalid {background-image: url(invalid.png); box-shadow: 0px 0px 5px #b01212; border: 2px solid #b01212;}
input:valid:required {background-image: url(accept.png); border: 2px solid #7ab526;}
div label {width: 100%;}
</style>
</head>
<body>
<div id="frmProduct">
    <!-- simple form for query keyword entry -->
    <form name="addItem" action="addItem.php" method="post">
    <fieldset>
    <legend>Add Item</legend>
    <ol>
      <li>
        <label for="title">Title</label>
        <input autofocus required id="title" name="title" value="Great Black Headphones" maxlength="80" />
      </li>
      <li>
        <label for="categoryID">Category ID</label>
        <input required id="categoryID" name="categoryID" value="112529"/>
      </li>
      <li>
        <label for="startPrice">Start Price</label>
        <input required id="startPrice" name="startPrice" value="20.00"/>
      </li>
      <li>
        <label for="pictureURL">Picture URL</label>
        <textarea rows="4" cols="40" required id="pictureURL" name="pictureURL">http://www.monsterproducts.com/images_db/mobile/MH_BTS_ON-SOHD_BK_CT_glam.jpg</textarea>
      </li>
      <li>
        <label for="description">Description</label>
        <textarea rows="4" cols="40" required id="description" name="description">A great pair of brand new black headphones - one for each ear.</textarea>
      </li>
    </ol>
    <input type="submit" value="Add Item">
    </fieldset>
    <br/>
  </form>
</div>
<div id="container">
  <?php
        // Display information to user based on AddItem response.

        // Convert the xml response string in an xml object
        $xmlResponse = simplexml_load_string($response);

        // Verify that the xml response object was created
        if ($xmlResponse) {
            echo "hi";
            // Check for call success
            if ($xmlResponse->Ack == "Success") {

                // Display the item id number added
                echo "<p>Successfully added item as item #" . $xmlResponse->ItemID . "<br/>";

                // Calculate fees for listing
                // loop through each Fee block in the Fees child node
                $totalFees = 0;
                $fees = $xmlResponse->Fees;
                foreach ($fees->Fee as $fee) {
                    $totalFees += $fee->Fee;
                }
                echo "Total Fees for this listing: " . $totalFees . ".</p>";

            } else {

                // Unsuccessful call, display error(s)
                echo "<p>The AddItem called failed due to the following error(s):<br/>";
                foreach ($xmlResponse->Errors as $error) {
                    $errCode = $error->ErrorCode;
                    $errLongMsg = htmlentities($error->LongMessage);
                    $errSeverity = $error->SeverityCode;
                    echo $errSeverity . ": [" . $errCode . "] " . $errLongMsg . "<br/>";
                }
                echo "</p>";
            }

        }
    ?>
</div>
</body>
</html>

tradingConstants.php contains this:

DEFINE("SITEID",203);

// production vs. sandbox flag - true=production
DEFINE("FLAG_PRODUCTION",false);

// eBay Trading API version to use
DEFINE("API_COMPATIBILITY_LEVEL",865);

and sandbox key values.