Sucuri is serving up some kind of Javascript redirection page to us..
<html><title>You are being redirected...</title>
<noscript>Javascript is required. Please enable javascript before you are allowed to see this page.</noscript>
<script>var s={},u,c,U,r,i,l=0,a,e=eval,w=String.fromCharCode,sucuri_cloudproxy_js=\'\',S=\'cz0iMCIgKyAiIiArIjZzdSIuc2xpY2UoMCwxKSArICAnJyArJycrJ3JRMycuY2hhckF0...
You'll need to whitelist or somehow allow these requests to /index.php?app=core&module=system&controller=marketplace to reach your origin.