Apple has stopped supporting older Safari extensions. If you currently have an older version of the Button for Safari, you’ll need to install the new version from the App Store.
The new version of the Button is compatible with macOS 10.13 or later and Safari 11 or later. You can also install the Button for Chrome, Edge and Firefox.
To install the latest version of the Button for Safari:
Look for the Rakuten Cash Back Button by searching for Rakuten Cash Back in the search box.