I've have a problem when I call my Salesforce API, this function "openssl_pkey_get_private" return false. The key is well installed and fully functionnal. The dev who I work with doesn't have this problem on a OVH mutualise server.
This seems to be a PHP question. Maybe you can post it on StackOverflow or one of the StackExchange sites All Sites - Stack Exchange . It is not really related to Plesk.