Your website is not using a custom 404 error page. Default 404 error pages result in a poor experience - it can mislead users into thinking an entire site is down or broken, greatly increases the chance they leave your site entirely, and looks unprofessional. By creating a custom 404 error page, you can improve your website's user experience by letting users know that only a specific page is missing/broken (and not your entire site), providing them helpful links, the opportunity to report bugs, and potentially
track the source of broken links in your site.