For future peoples possibly encountering this same error:

"stream_socket_client(): SSL operation failed with code 1. OpenSSL Error messages: error:14094410:SSL routines:ssl3_read_bytes:sslv3 alert handshake failure stream_socket_client(): Failed to enable crypto stream_socket_client(): unable to connect to ssl://some.site:443 (Unknown error)

I was getting this on a server that was running PHP 7.1.  Upgrading to 7.3 resolved it.

(I also enabled SSL on the site that the call was being made from – a test site so it didn’t previously have any SSL – but I don’t think that made any difference.)