You should make the default URL SSL from our setting panel.
Current CLICKBANK INTEGRATION URL is http not https.
"Configuring Your URL
Once you have received access to the Instant Notification feature, you must create a target URL and a program to process the Notifications that will be sent to your URL. You can use ports 80 or 443.
Transport Layer Security (TLS) and Secure Socket Layer (SSL)
It is strongly recommended that you utilize this feature with Transport Layer Security (TLS) or Secure Socket Layer (SSL) enabled. Using this feature without TLS or SSL enabled can expose your sales data to thieves. However, because credit card and bank information is not transmitted via the Instant Notification service, we do not require you to use TLS or SSL to encrypt Instant Notification transmissions.
NOTE – You cannot use a self-signed SSL certificate. You must use a valid certificate."