title: Amazon MWS API using PHP shows no Result
body: <p>I have been using amazon mws API for developing a project to find Lowest Priced offers, It works fine with action ListMatchingProducts and GetMatchingProduct but when it comes to GetLowestPricedOffersForASIN, it shows no result in XML output</p>
  
  <p>"This XML file does not appear to have any style information associated with it. The document tree is shown below."</p>
  
  <p><strong>My PHP File Here:</strong>
  <div class="snippet" data-lang="js" data-hide="false">
  <div class="snippet-code">
  <pre class="snippet-code-css lang-css prettyprint-override"><code>&lt;?php
  $param = array();
  $param['AWSAccessKeyId']   = ''; 
  $param['Action']           = 'GetLowestPricedOffersForASIN';
  $param['SellerId']         = ''; 
  $param['SignatureMethod']  = 'HmacSHA256';  
  $param['SignatureVersion'] = '2'; 
  $param['Timestamp']        = gmdate("Y-m-d\TH:i:s.\\0\\0\\0\\Z", time());
  $param['Version']          = '2011-10-01'; 
  $param['MarketplaceId']    = 'ATVPDKIKX0DER'; 
  $param['ItemCondition']    = 'used';
  $param['ASIN']      = '0439139600';
  $secret = '';
  $url = array();
  foreach ($param as $key =&gt; $val) {
  
   $key = str_replace("%7E", "~", rawurlencode($key));
   $val = str_replace("%7E", "~", rawurlencode($val));
   $url[] = "{$key}={$val}";
  }
  
  sort($url);
  
  $arr   = implode('&amp;', $url);
  
  $sign  = 'GET' . "\n";
  $sign .= 'mws.amazonservices.com' . "\n";
  $sign .= '/Products/2011-10-01' . "\n";
  $sign .= $arr;
  
  $signature = hash_hmac("sha256", $sign, $secret, true);
  $signature = urlencode(base64_encode($signature));
  
  $link  = "https://mws.amazonservices.com/Products/2011-10-01?";
  $link .= $arr . "&amp;Signature=" . $signature;
  $ch = curl_init($link);
  curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-type: application/xml'));
  curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
  curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE); 
  $response = curl_exec($ch);
  $info = curl_getinfo($ch);
  curl_close($ch);
  header('Content-type:text/xml');
  echo $response;</code></pre>
  </div>
  </div>
  
  I can't put AWSAccessKeyID, Secret and SellerID here...</p>