title: Amazon Product API: ItemLookup with Multiple ASINs
body: <p>So I'm having a bit of trouble figuring out why I get a particular error. [NOTE: I've masked my AccessKey and Signature parameters]</p>
  
  <p>The url below returns <strong>valid</strong> xml for ONE product. </p>
  
  <pre><code>http://ecs.amazonaws.com/onca/xml?AWSAccessKeyId=[myAccessKey]&amp;IdType=ASIN&amp;ItemId=B002UD52WQ&amp;Operation=ItemLookup&amp;ResponseGroup=Medium&amp;Service=AWSECommerceService&amp;Timestamp=2010-07-27T23:17:57.000Z&amp;Signature=[mySignature]
  </code></pre>
  
  <p>However, when I use the url below to look up multiple ASINs by comma-separating the ASIN IDs, I get an error</p>
  
  <pre><code>http://ecs.amazonaws.com/onca/xml?AWSAccessKeyId=[myAccessKey]&amp;IdType=ASIN&amp;ItemId=B002UD52WQ,B002C0CZEU&amp;Operation=ItemLookup&amp;ResponseGroup=Medium&amp;Service=AWSECommerceService&amp;Timestamp=2010-07-27T23:17:57.000Z&amp;Signature=[mySignature]
  </code></pre>
  
  <p>ERROR Message:</p>
  
  <blockquote>
    <p>The request signature we calculated
    does not match the signature you
    provided. Check your AWS Secret Access
    Key and signing method. Consult the
    service documentation for details</p>
  </blockquote>
  
  <p>Anyone know why this is happening? Thanks in advance.</p>
  
  <p>DOCUMENTATION CAN BE FOUND <a href="http://docs.amazonwebservices.com/AWSECommerceService/latest/DG/index.html?ItemLookup.html" rel="noreferrer">HERE</a> <em>"To look up more than one item at a time, separate the item identifiers by commas."</em></p>