404.php file not loading

I’m trying to get a nice 404 error page to display, I have a 404.php file in my custom template directory but whenever I type a URL that doesn’t exist I get the standard 404:
https://ewebsiteservices.com/pagedoesntexist

I was reading around and I found that this below URL is supposed to show the 404.php file, but it just goes to the default home page.
https://ewebsiteservices.com/index.php?error=404

I put this in my .htaccess
ErrorDocument 404 /index.php?error=404

I have a default Page and Posts in my Reading Settings.

Permalinks is enabled.

Any help is appreciated. Thanks.