404.php doesn’t seem to work for me.

Hi Folks,

I have a 404.php file included in a theme I’m building, but it doesn’t seem to be working for some reason.

My code for this file is very basic as follows:

<?php get_header(); ?>
<?php get_sidebar(); ?>

	<div id="mainContent" class="column">

		<h2 class="center">Error 404 - Not Found</h2>
           </div>

<?php get_footer(); ?>

My url for the theme is https://really-valid-info.com/blog/
I’ve tried browsing to a non existent page such as https://really-valid-info.com/blog/?page_id=25 This produces a page, but without any text or message!

The same thing happens when I switch to using the default theme – so not sure how to get this to work!

Any advice would be appreciated.

Many thanks,

Myles