If you find that your Register or Login buttons won't open, and you have your site set with www in the domain, this tutorial should help. 

• Click Settings and choose URL match.

• Click Enable and then clear cache.

If the above doesn't help, here are a few threads from our community:

https://community.phpfox.com/forum/thread/53970/login-not-working-v4-2/?view=332727

https://community.phpfox.com/forum/thread/52764/short-url-problem-solved/