IN_DEV mode loads the data from different locations/files (js, CSS, templates, etc) and requires uploading a separate zip package with the extra files.

You really shouldn't enable it on a production site. If you need it, setup a test site somewhere else not accessible by everyone (either locally or behind a htaccess check maybe).

Thanks for the response, I have installed the correct files. But it's trying to load in a stylesheet that does not exist, which is way the styling looks off on my website. It's passing "https://test.higherlevel.nl/applications/core/interface/css/css.php?css=applications/core/dev/css/global/framework/1-1-reset.css,applications/core/dev/css/global/framework/1-2-settings.css,applications/core/dev/css/global/framework/1-3-variables.css,applications/core/dev/css/global/framework/1-4-colors.css,applications/core/dev/css/global/framework/1-5-global.css,applications/core/dev/css/global/framework/3-badges.css,applications/core/dev/css/global/framework/3-boxes.css,applications/core/dev/css/global/f...re/dev/css/global/framework/prettify.css,applications/core/dev/css/global/framework/spectrum.css,applications/core/dev/css/global/framework/streams.css,applications/core/dev/css/global/framework/table-of-contents.css,applications/core/dev/css/global/framework/tables.css,applications/core/dev/css/global/framework/tabs.css,applications/core/dev/css/global/framework/tags.css,applications/core/dev/css/global/framework/toolbox.css,applications/core/dev/css/global/framework/typography.css&v=dce2e8dfbc1741358609"

This stylsheet isn't being recognized and the link buildings looks off.
"applications/core/dev/css/global/f...re/dev/css/global/framework/prettify.css"


Could this be because my core files are corrupted?

Those URLs are correct for IN_DEV, but my guess it that the URL is too long and your server stops it from loading the content.

I've seen it happen sometimes and you must increase a URL length variable (which I don't recall the name of right now).

This sadly did not work. It's still not loading in the styling of the website in debug mode even though I have added this:

•  LimitRequestFieldSize 16384

• LimitRequestLine 10000
   
   

What error do you get when you try to open that link yourself in the browser? I'd try myself but I'm locked out by an htaccess password request.

This is the error which i'm getting when I open the link in the browser. Thanks for taking the time to to take a look.

Also when I try to navigate to "Applications" in the admin panel, I get this error.

I have managed to fix the CSS issues, but the issue where the array key "application_title" in undefined still persists.