Turns out that my Modpack files weren't laid out correctly.
Didn't find that out until I actually asked through the support stuff..
And only now I get notifications about why it wasn't accepted... Took it's time..
I just uploaded a modpack through the 'file' tab.
It sat there saying 'Under review' and now it's completely disappeared.
I've gotten no message saying there's a problem or anything, so I'm not sure what's happening.