Cannot see errors in Codeigniter project

I see the HTTP ERROR 500 too, but just on the page itself, not with a redirect. This gives me the idea that the .htaccess rules are now working, and this is a PHP code crash.

Usually, the place to start with these issues is to enable error messages so you can see why the PHP code crashed:

I did go ahead and test this for you. It seems that there is some configuration in your site that uses file paths that uses backslashes instead of forward slashes. If you developed the site on Windows, that would be the way to do it. But our servers run Linux, which uses forward slashes for directories, not backslashes, so the paths do note work. Please update your site’s configuration to use forward slashes, not backslashes, in file paths.