Magento Patch SUPEE-8167 for PayPal Instant Payment Notifications
For increased security, merchants will only be able to use HTTPS when posting messages back to PayPal via their Instant Payment Notification (IPN) service. In the past, PayPal has allowed the use of HTTP for these postbacks. As of June 30, 2017, PayPal Instant Payment Notifications will no longer allow HTTP to post messages back to PayPal for verification. To comply with these changes, all Magento merchants using PayPal must upgrade or implement the Magento Security Patch SUPEE-8167.