title: Amazon Pay on Woocommerce error in Sandbox mode (InvalidOrderReferenceId)
body: <p>I installed  the Amazon Pay plugin on my WordPress/Woocommerce website, left in in Sanbox mode, created a Sandbox test account and when I run a test transaction, I get a message that states &quot;Invalid Payment Method&quot;</p>
  <p>When I go to the Woocommerce log, the error that I find is:</p>
  <pre><code>&lt;ErrorResponse xmlns=&quot;http://mws.amazonservices.com/schema/OffAmazonPayments/2013-01-01&quot;&gt;
    &lt;Error&gt;
      &lt;Type&gt;Sender&lt;/Type&gt;
      &lt;Code&gt;InvalidOrderReferenceId&lt;/Code&gt;
      &lt;Message&gt;The OrderReferenceId S00-0000000-0000000 is invalid.&lt;/Message&gt;
    &lt;/Error&gt;
    &lt;RequestId&gt;646d0e3e-b603-420d-8178-ad20690fee41&lt;/RequestId&gt;
  &lt;/ErrorResponse&gt;
  </code></pre>
  <p>Any ideas?  Thank you!</p>