What is the difference between HTTPS and HTTP websites for Web Push Notifications

Your website visitors can only subscribe to push notifications through an HTTPS website so that your notifications are delivered securely. If your website is not enabled for HTTPS, please contact your website host to obtain and SSL certificate. 

An HTTPS website (one starting with https://) is more secure and protects personal data. This type of website has something called an SSL certificate that works to encrypt your data so that private information cannot be read by outsiders.