Installing Invoiceplane in a subfolder - "404 Error"

Please have a look at:

demo.invoiceplane.com/demo

The used htaccess is:

<IfModule mod_rewrite.c>
  RewriteEngine On

  ### uncomment to force HTTPS
  RewriteCond %{HTTPS} off
  RewriteRule ^(.*)$ https://%{HTTP_HOST}/$1 [R=301,L]

  RewriteRule ^index\.php$ - [L]
  RewriteCond %{REQUEST_FILENAME} !-f
  RewriteCond %{REQUEST_FILENAME} !-d
  ### uncomment and adjust if installed in subdirectory
  RewriteRule . /demo/index.php [L]
</IfModule>

You can PM me with your real Domain and I will try to help you.