title: 4020 error on refund in MySagePay
body: <p>When trying to refund a transaction on MySagePay (test mode, haven't tried live) I keep receiving the following error:</p>
  
  <blockquote>
    <p>Failed refund attempt via My Sage Pay screens by <em>[redacted]</em>. Error returned was: 4020 : Information received from an Invalid IP address.</p>
  </blockquote>
  
  <p>Since the information should be being received from Sage's IP addresses, I'm not sure why this is happening or how to fix it.</p>
  
  <p>I've tried adding whitelisting the IP for <code>test.sagepay.com</code> and tried whitelisting my own computer's IP but neither worked.</p>
  
  <p>Is this another case of Sage sending misleading error messages?</p>
  
  <ul>
  <li>If so, what steps can I take to find out the real cause?</li>
  <li>If not, what IP addresses do I need to whitelist to make their control panel work?</li>
  </ul>