The 400 (Bad Request) status code indicates that the server cannot or will not process the request because the received syntax is invalid, nonsensical, or exceeds some limitation on what the server is willing to process. It means that the request itself has somehow incorrect or corrupted and the server couldn't understand it. The server is refusing to service the request because the entity of the request is in a format not supported by the requested resource for the requested method . Therefore, it prevents the website from being properly displayed. The main thing to understand is that the 400 Bad Request error is a client-side error.

The cause of 400 Bad Request error can be a wrongly written URL or a URL that contains unrecognizable characters. Another cause of the error might be an invalid or expired cookie. Also, if you try to upload a file that's too large. If the server is programmed with a file size limit, then you might encounter a 400 error.

Expired Client Certificate

This issue typically happens for a 2-Way TLS, when the certificate sent by the client is expired. In a 2-way TLS, both client and server exchange their public certificates to accomplish the handshake. The client validates the server certificate and the server validates the client certificate. During the TLS handshake if it is found that the client certificate is expired, then the server will send 400 - Bad request with the message "The SSL certificate error". The solution for this problem is that procure a new certificate and upload the certificate

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