could you log onto your backen and look at the error log you will probably find the issue there. If you are using a VPN and still get a 403 then it should be ip related. I would just check ip logs still and look at server logs to see the reason if you are running php perhaps also have a look at that too. Also web hosting services and security are getting smart enough to detect proxies and vpns so some bloak them by default.
Yeah, a new non VR SP IP or a sequel would be best. They can't count to 3 so a sequel doesn't seem likely. Portal is my favourite and would love a sequel but don't expect one. I think I'll take whatever if they bring it on consoles too. Might go for VR as well.