Cannot get Multisite working properly

I'm trying to migrate multiple individual installs to a multisite, Sub-domains are setup, but only the main site is functioning. Trying to get to the subsites generates a 403 error. I've tried resetting permissions and manually setting permissions to 644/755, neither attempt fixed the issue.

I try to use a subfolder install, then subsites will appear, but the dashboards do not load properly, and I can't make edits to them. My hosting provider tells me that everything should be fine for multisite, but since that's not something they provide as an install, they can't give help on.