When a user requests to view a webpage and enter the domain in a web browser and the web server denies the request, the user receives the 404 Not Found error or This site can't be reached.
A "404 Not Found" error is a standard HTTP response code indicating that the server could not find the requested resource, typically a web page. This error occurs when a user tries to access a URL that doesn't exist on the server. It can be caused by several factors 
How to Fix the 404 Not Found Error?
1. Clear Your Browser Cache and Cookies:
* Clearing your browser’s cache and cookies can sometimes resolve this issue. This forces the browser to re-request all the site files and log you out from all websites.
2. Check DNS records:
* Firstly check whether the A and NS records are properly pointed or not for that you can use this link to check dns records.
https://intodns.com/ or https://dnschecker.org/
if records are not pointed then point records in the dns zone file.
* Mostly this error is resolved by using this solution.
3. Try uploading an Index Page:
* When you visit your website, the website’s homepage name should be named index.html or index.php.
* If not, resolve this by uploading an index page to your httpdocs or public_html directory.
* Open the .htaccess file. Insert the following code snippet to redirect index.php or index.html to your existing homepage. Make sure the name of your page appears in lieu of homepage.html.
Redirect /index.html /homepage.html
* Try to view the homepage of your website after adjusting the web server settings to check if the issue has been fixed.
4. File and Directory Permissions:
* Check the Directory and Files permissions, it should be 755 for directories and 644 for files.
5. Checking Wordpress Plugin:
* Navigate to public_html >> wp-content. And disable the folder "plugins" by renaming it. e.g plugins.bk.
* Now access your website, if its not showing any error then there is an issue with one of the plugin.
* To activate all of the plugins again, rename the folder "plugins".
* Go through your WordPress dashboard and disable each plugin one at a time to see if the site is operating properly. This can help in identifying the problematic plugin.
Once found, update the plugin or think about removing it to resolve the problem.
6. Scan for Malware:
* Malware-infected WordPress websites can constantly upload unwanted code into the.htaccess file,
Therefore, no matter how hard you attempt to fix the .htaccess file, the issue will still occur.
7. Contact our Support:
* If you're unable to identify the problem after all these steps, please get in touch with us by clicking Support on the left and opening a support request.
Important Note: Always make backups before making changes to your website, so you can easily restore it to a previous state if necessary.