Accessing Codeigniter folder inside WordPress directory

Solution:

You just need to add a question mark after the index.php like so:

RewriteRule ^(.*)$ index.php?/$1 [L]

So the full thing (in your CodeIgniter .htaccess file is like:

<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteRule ^(.*)$ index.php?/$1 [L]
</IfModule>