4xx status codes refer to the HTTP (Hypertext Transfer Protocol) status codes that indicate that there was an error on the client side when making the request to the server. These status codes indicate that the server could understand the request, but the request was invalid or could not be fulfilled.
The most common 4xx status codes are:
400 Bad Request: The request is malformed or invalid. This can happen when the client sends an incomplete request or when the request is not in the correct format.
401 Unauthorized: The request requires user authentication, but the client did not provide valid authentication credentials.
403 Forbidden: The server understands the request, but the client does not have the necessary permissions to access the resource.
404 Not Found: The server cannot find the requested resource. This can happen when the client requests a page that does not exist on the server.
Other 4xx status codes are:
405 Method Not Allowed: The client used a request method not supported by the server.
408 Request Timeout: The client took too long to send the request, and the server closed the connection.
410 Gone: The requested resource is no longer available and will not be available again.
4xx status codes indicate that the client has made an error when making the request and that the server cannot fulfil the request. Webmasters and website owners should monitor these status codes, as they can indicate issues with the website, such as broken links, missing pages, or problems with user authentication.
Also, See: 2xx Status Code