SSL Error 503: Backend unavailable

Hi, I don't get how to solve this problem. I'm trying to install my SSL but get this error (I can access if I type the IP directly instead of using a gateway with the domain). I'm currently running apache on xampp but I can't find anything about this problem. Can someone help me? I have tried disabling firewall and no way I made it work. I called support and they told me it has something to do with vhosts and stuff but don't know where and what should I add/change... any experienced in this that can help me? My domain is alfarust.eu and what I use is apache (last version I suppose). Thank you.