1. When using a router you recieve 403 - Check the server elogs where it'll say that CSRF has blocked the request from the router as it's not a part of the whitelisted allowed URLs.
2. Once you add the router URL to the whitelisted URL's list in 'Home ->....-> Configure Allowed Referer', you need to restart the server.
3. If you are able to view some options of adminui, then probably the logged in user doesn't have proper roles assigned to him/her.