After a change from http to https of my website, some connections cannot be established. Error message: HTTP de WP : cURL error 35: error:140770FC:SSL routines:SSL23_GET_SERVER_HELLO:unknown protocol.

Here is the fix... Almost. (French)

To install an SSL certificate on your virtual private server, the first step is to generate a key for the Certificate Signing Request (CSR). If the certificate will be used by service daemons, such as Apache, Postfix, Dovecot, etc, a key without a passphrase is often appropriate.