Detect error 404 page to find out the issue

Question

I have a wordpress website, which when I visit

www.mywordpress.com/test/setup

it throws an error 404 page.

Which class in wordpress handles the request dispatching?

Answer 1

404 errors are handled browser site and has nothing to do with Wordpress. When nothing is returned from the request, the browser triggers a 404 action and displays a 404 not found error page

By default, if no custom 404 page exists on the site, the browser will display its own default 404 page.

For further reading, check out: Creating an Error 404 page