The parameters for the EsendexSubscriptionService constructor include optional arguments for a security certificate:
EsendexSubscriptionService( $username, $password, $account, $isSecure = false, $certificate = '' )
To send via HTTPS, use the following arguements:
$isSecure = true
$certificate = "PATH TO CERTIFICATE FILE" ( e.g. C:\Windows\curl_ca_bundle.crt )
To send via HTTP, these arguments can be ignored.
For a successful request, results are in the format:
Result=OK ContactID=valuewhere value is the the contact ID for the contact related to the subscription. If the subscription relates to a non-contact for the account, an empty Guid is returned.
For an unsuccessful request, results are in the format:
Result=Error Message=value where Message value is a URL encoded description of the error.