When you encounter this error when generating an SSL certificate it’s because of a configuration issue with OpenSSL. OpenSSL is a library commonly used to interact with TLS and SSL. An error in this library can cause issues like the RSA keypair export failure.
Really Simple SSL does not manage the OpenSSL library on your webserver. OpenSSL is managed by your hosting provider. We, therefore, recommend contacting your hosting provider about this as they can update OpenSSL.