New .htaccess breaks site - .htaccess

Question

I'll admit I'm brand brand new to coding. I am trying to help a client who uses Dreamweaver to publish their website on a server at their headquarters. I asked their IT department to add code to their .htaccess file that would help redirect non https to https and force www but also remove the .html extensions. I am pretty sure the code is correct but when they added it, the site broke.
The old .htaccess file had the following code:
/var/www/html/HRT/.htaccess
RedirectMatch 301 ^/here(/.+?)?$ http://go.example.com/here
RedirectMatch 301 ^/HERE(/.+?)?$ http://go.example.com/here
RedirectMatch 301 ^/there(/.+?)?$ http://go.example.com/there
RedirectMatch 301 ^/THERE(/.+?)?$ http://go.example.com/there
I changed the urls for privacy. Just having this worked before. But when I asked them to add the below code, it broke. Not sure even where to start.
# FORCE HTTPS, FORCE WWW and REMOVE HTML #
RewriteEngine On
RewriteCond %{HTTPS} off [OR]
RewriteCond %{HTTP_HOST} !^www\. [NC]
RewriteCond %{HTTP_HOST} ^(?:www\.)?(.+)$ [NC]
RewriteRule ^ https://www.%1%{REQUEST_URI} [L,NE,R=301]
RewriteRule ^([^/]+)\.html$ $1 [QSA,L]
# EXPIRES CACHING VIA HTACCESS #
<IfModule mod_expires.c>
ExpiresActive On
ExpiresByType image/jpg "access 1 year"
ExpiresByType image/jpeg "access 1 year"
ExpiresByType image/gif "access 1 year"
ExpiresByType image/png "access 1 year"
ExpiresByType text/css "access 1 month"
ExpiresByType text/html "access 1 month"
ExpiresByType application/pdf "access 1 month"
ExpiresByType text/x-javascript "access 1 month"
ExpiresByType application/x-shockwave-flash "access 1 month"
ExpiresByType image/x-icon "access 1 year"
ExpiresDefault "access 1 month"
</IfModule>
I should note that during the previous week they added to their http.config file for expiring cache too so I'm not sure that would cause this problem. Just trying to think of all the things they've done before this error.
Thanks in advance.

Answer 1

RewriteRule ^([^/]+)\.html$ $1 [QSA,L]
You can't simply "remove" the .html file extension like that in .htaccess - it will most certainly break your site.
In fact, you can't remove the file extension by editing .htaccess alone. It's a two stage process:
You need to remove the .html extension on all your URLs - in your application. All your internal links need to be updated to omit the .html extension.
You then use .htaccess to internally rewrite the request without an extension, back to the real filesystem path that includes the .html extension. Underneath it all, your filesystem paths have not changed.
For example:
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^([^.]+)$ $1.html [L]
This assumes that your URLs do not otherwise contain dots (.) - except if they are requesting a file directly (eg. .js, .css, .jpg, etc.)
You will also need to ensure that MultiViews is disabled (if not already) for this to work properly. ie. Include the following at the top of your .htaccess file:
Options -MultiViews
If you are changing an existing URL structure then you'll need to implement an external redirect to physically remove the .html extension from the URL in order to preserve SEO. However, you should only implement this if you have completed step #1 (and #2) above and removed the .html extension on all your internal URLs (otherwise your users will suffer an external redirect on every link when navigating your site, which will be slow and double the requests hitting your server).
For example, the following redirect would need to go before the rewrite (above):
RewriteCond %{ENV:REDIRECT_STATUS} ^$
RewriteRule (.+)\.html$ /$1 [R=302,L]
The condition that checks against the REDIRECT_STATUS environment variable ensures that we target only direct requests and not the rewritten request.
Note that this is currently a 302 (temporary) redirect. Only change it to a 301 (permanent) redirect once you have confirmed that it works OK - in order to avoid caching issues.
In Summary
# Disable MultiViews
Options -MultiViews
Then add the following below your canonical HTTP to HTTPS and non-www to www redirects:
# Redirect to remove the ".html" extension from direct requests
RewriteCond %{ENV:REDIRECT_STATUS} ^$
RewriteRule (.+)\.html$ /$1 [R=302,L]
# Internal rewrite to re-append the ".html" extension for the internal request
# NB: Exclude requests for directories
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^([^.]+)$ $1.html [L]