Hi there,
I went ahead and applied the changes on /wp-content/plugins/x-email-mailchimp/email-mailchimp/fuctions/vendor/mcapi/Mailchimp.php
The fix is just this
curl_setopt($this->ch, CURLOPT_SSL_VERIFYPEER, false);
But it was added in the wrong place. Should be added along with other curl_setopt() instances. I checked and subscription is now going through.
Cheers!