Multi-Domains plugin – Sites show an Index page

I installed the Multi-Domains plugin, added a second domain, and followed the instructions. In the DNS records for the second domain, I added a wildcard subdomain that points to my WP installation by IP, and I made sure my site is the default for my dedicated IP. But now whenever I add a site under the second domain and I try to go to it, this shows up:

Index of /


Apache Server at Port 80

Also, I have the second domain as an addon domain on my hosting account… I tried to do it as a parked domain but I don’t think that’s included in my plan. Am I supposed to add it as an addon domain, parked, or none at all? I’m pretty new at this stuff… I hope someone can help me.