Users can't login when using www. of the site.

I am using smf 2.09 .

I want to force users to use my site with www.

I want this because my cloudflare is configured to be used with www.



Anyways, when using www. , I notice that users can't login for some reason. The error just says "wrong user/passwo...



Users can't login when using www. of the site.