You might encounter an ERR_SSL_VERSION_OR_CIPHER_MISMATCH error when visiting your website over HTTPS/SSL. This error is also known as SSL_ERROR_NO_CYPHER_OVERLAP in Mozilla Firefox.

This error means that the server and client (browser) are unable to establish a secure connection between them. To establish a secure connection between the server and client, they need to have a cipher in common to understand each-others messages. If the ciphers don’t match, the server and client can’t communicate and it results in this error message.

The first step in debugging this issue is to check whether the issue occurs in multiple browsers. If the error occurs in just one browser, try to update the browser and clear the browser’s cache. If that doesn’t solve the issue, it likely has to do with a lack of defined ciphers in the server configuration. Update the available ciphers in the server configuration to solve this error. This is something your hosting provider can help with, they will have access to the server configuration and can make the necessary changes for you.

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