The 400 error code occurs primarily when the request sent to the HTTP server had invalid syntax. This usually happens when a user types the wrong URL in a browser’s address bar.

The 401 error code is usually displayed when the URL requires authentication and the user trying to connect cannot be verified through the requested information: username and password.

In this case, the error code 403 indicates that a valid request to display the site was made, but the server is prohibited from executing the request because of lack of permission from the administrator.

This is one of the most common error codes that users encounter on the internet and means that the user is trying to log in to a page on your site that no longer exists. These errors also negatively affect the SEO performance of your website.

This error code is just a generic error message that can cover many server issues that another 5XX error could often better categorize.

Error 502 occurs when a user request was received, but an internal server error prevented the action from completing. Once again, this website error message has several possible causes.

A 504 error code is displayed when the requesting server did not receive a timely response from the receiving server when attempting to load the page.