This has nothing to do with Hostgator or Really Simple SSL. It’s just that if you have a site without a certificate for the www version (which is not a best practice!) the site obviously can’t load over www.
The best solution of course is to add www to the certificate. If, for some reason this is not possible, you could use a (not recommended, because less secure) workaround by adding a redirect from www to non www in the .htaccess.
I’ve explained here why you shouldn’t do this, and how you can do it if you want to do this anyway.
https://really-simple-ssl.com/knowledge-base/avoid-landing-page-redirects/
Hostgator will charge another $25 for the www version.
I finally just found on the Hostgator knowledge base that Hostgator suggests a different SSL plugin (Insecure Content Fixer). I tried it and it seems to be working. It may not be as thorough as Really Simple SSL but it works with Hostgator apparently.
Thanks!
It works because it does not redirect the www domain to https apparently.
It does redirect if Really Simple SSL is NOT activated. Even without the redirect in the htaccess file.
What is happening, is that WordPress is now handling the redirect. If you don’t have www in the certificate, and it works, it can’t be redirecting to https://www, as this would cause the error you saw. Instead, it will be redirecting like this: http://www.domain.com -> http://domain.com -> https://domain.com
Which bypasses the www, as described in the article I posted before.