Then why do you mention: Error 403 means your license key is not valid.
When installing i get the same errors, so it makes perfectly sense.
What I meant is that your comment that "The license server is not working at all for V3" makes no sense, because the download server doesn't consult the licensing system at all. It consults the billing system, which is independent, and if the billing system wasn't working we'd know about that pretty quickly.
Whether the licensing servers are up or down, the file server won't be affected.
A code 403 means your v3 account package is either suspended, terminated, or nonexistent (eg: bad key) in our billing system.
If you're having problems with a specific key, send me the license key via PM and I'll look into it. To be clear, though, we have a lot of people regularly installing v3 for testing (some staff, some clients who have been designated official testers) and the download system is definitely working just fine.