This is a temporary error that has now started to appear when the Activator is first installed or updated.
1. Remove the Activator and plugin.
2. Clear the site cache with the plugins that create it.
3. Install the Activator again and activate it.
4. Install and activate the WP Rocket plugin.
If a warning Error appears, log in to the site on the login page, entering your Username and Password.
5. Go to the plugin settings and delete the site cache again.
The site should work normally.