ERROR 403: one page on the site always leads me to 403

My site has a .htaccess file to stop the .html name from appearing in the search bar, so it looks more professional. All my links, except for one, work perfectly. That one requires me to type in the .html, or else it redirects me to the 403 page. here is my .htaccess file:

RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^([^\.]+)$ $1.html [NC,L]

What is wrong with my page?

please read all

OxyDac said:
please read all

My .htaccess file is correct

Does this script contain name such as “chat.html”?

There are name constraint AFAIK, I don’t have the full list, but surely that is one of many names which is not allowed here.