Я не получаю цены с помощью Amazon Product Advertising API

Пытаюсь получить цены по ASIN номеру с помощью Amazon Product Advertising API.

Код:

    $artNr = "B003TKSD8E";
    $base_url = "http://ecs.amazonaws.de/onca/xml";
    $params = array(
        'AWSAccessKeyId' => self::API_KEY,
        'AssociateTag' => self::API_ASSOCIATE_TAG,
        'Version' => "2010-11-01",
        'Operation' => "ItemLookup",
        'Service' => "AWSECommerceService",
        'Condition' => "All",
        'IdType' => 'ASIN',
        'ItemId' => $artNr);


    $params['Timestamp'] = gmdate("Y-m-d\TH:i:s.\\0\\0\\0\\Z", time());

    $url_parts = array();
    foreach(array_keys($params) as $key)
        $url_parts[] = $key . "=" . str_replace('%7E', '~', rawurlencode($params[$key]));
    sort($url_parts);

    $url_string = implode("&", $url_parts);
    $string_to_sign = "GET\necs.amazonaws.de\n/onca/xml\n" . $url_string;

    $signature = hash_hmac("sha256", $string_to_sign, self::API_SECRET, TRUE);

    $signature = urlencode(base64_encode($signature));

    $url = $base_url . '?' . $url_string . "&Signature=" . $signature;

    $response = file_get_contents($url);
    $parsed_xml = simplexml_load_string($response);

Я думаю, что это должно быть правильно - но я не получаю предложений в ответе:

<?xml version="1.0" ?>
  <ItemLookupResponse xmlns="http://webservices.amazon.com/AWSECommerceService/2010-11-01">
    <OperationRequest>
      <RequestId>*********************</RequestId>
      <Arguments>
        <Argument Name="Condition" Value="All">
      </Argument>
        <Argument Name="Operation" Value="ItemLookup">
      </Argument>
        <Argument Name="Service" Value="AWSECommerceService">
      </Argument>
        <Argument Name="ItemId" Value="B003TKSD8E">
      </Argument>
        <Argument Name="IdType" Value="ASIN">
      </Argument>
        <Argument Name="AWSAccessKeyId" Value="*********************">
      </Argument>
        <Argument Name="Timestamp" Value="2011-11-29T01:49:01.000Z">
      </Argument>
        <Argument Name="Signature" Value="*********************">
      </Argument>
        <Argument Name="AssociateTag" Value="*********************">
      </Argument>
        <Argument Name="Version" Value="2010-11-01">
      </Argument>
    </Arguments>
      <RequestProcessingTime>0.0083130000000000</RequestProcessingTime>
    </OperationRequest>
    <Items>
      <Request>
        <IsValid>True</IsValid>
        <ItemLookupRequest>
          <Condition>All</Condition>
          <IdType>ASIN</IdType>
          <ItemId>B003TKSD8E</ItemId>
          <ResponseGroup>Small</ResponseGroup>
          <VariationPage>All</VariationPage>
        </ItemLookupRequest>
      </Request>
      <Item>
        <ASIN>B003TKSD8E</ASIN>
        <DetailPageURL>http://www.amazon.de/Apple-iPhone-4-32GB-schwarz/dp/B003TKSD8E%3FSubscriptionId%3DAKIAI6NFQHK2DQIPRUEQ%26tag%3Dbanholzerme-20%26linkCode%3Dxm2%26camp%3D2025%26creative%3D165953%26creativeASIN%3DB003TKSD8E</DetailPageURL>
        <ItemLinks>
          <ItemLink>
            <Description>Add To Wishlist</Description>
            <URL>http://www.amazon.de/gp/registry/wishlist/add-item.html%3Fasin.0%3DB003TKSD8E%26SubscriptionId%3DAKIAI6NFQHK2DQIPRUEQ%26tag%3Dbanholzerme-20%26linkCode%3Dxm2%26camp%3D2025%26creative%3D12738%26creativeASIN%3DB003TKSD8E</URL>
          </ItemLink>
          <ItemLink>
            <Description>Tell A Friend</Description>
            <URL>http://www.amazon.de/gp/pdp/taf/B003TKSD8E%3FSubscriptionId%3DAKIAI6NFQHK2DQIPRUEQ%26tag%3Dbanholzerme-20%26linkCode%3Dxm2%26camp%3D2025%26creative%3D12738%26creativeASIN%3DB003TKSD8E</URL>
          </ItemLink>
          <ItemLink>
            <Description>All Customer Reviews</Description>
            <URL>http://www.amazon.de/review/product/B003TKSD8E%3FSubscriptionId%3DAKIAI6NFQHK2DQIPRUEQ%26tag%3Dbanholzerme-20%26linkCode%3Dxm2%26camp%3D2025%26creative%3D12738%26creativeASIN%3DB003TKSD8E</URL>
          </ItemLink>
          <ItemLink>
            <Description>All Offers</Description>
            <URL>http://www.amazon.de/gp/offer-listing/B003TKSD8E%3FSubscriptionId%3DAKIAI6NFQHK2DQIPRUEQ%26tag%3Dbanholzerme-20%26linkCode%3Dxm2%26camp%3D2025%26creative%3D12738%26creativeASIN%3DB003TKSD8E</URL>
          </ItemLink>
        </ItemLinks>
        <ItemAttributes>
          <Manufacturer>Apple Computer</Manufacturer>
          <ProductGroup>CE</ProductGroup>
          <Title>Apple iPhone 4 32GB schwarz</Title>/ItemAttributes>
        </Item>
      </Items>
    </ItemLookupResponse>

Может кто-нибудь объяснить мне, почему я не получаю никакой информации о ценах?

Большое спасибо