SSL_CTX_use_PrivateKey_file
The error message that you've provided means that the certificate and the Private key files used during the SSL installation don't match. In order to install the SSL certificate, it is required to have the matching certificate and Private key pair. Here's how to receive the matching certificate and key files: 1) generate CSR code on the hosting server; 2) back up the Private key file (yourdomain.key) that was generated along with this CSR; In case the matching Private key was lost or cannot be found, we suggest to reissue the certificate as follows: 1) generate a brand new CSR code; 2) back up the Private key from this latter generation; 3) reissue the certificate using the new CSR; 4) once the reissue is completed, install the newly issued certificate along with the Private key from the latter generated pair.