Browser notification must be allowed to subscribe.

Chrome Click the icon on the left of the browser search bar,
edit “Notifications” to be allowed, then refresh the page. Edge Click the "View Site Information" icon on the left side of the address bar,
then select "Allow" in the notification window that appears to receive notifications. Firefox Select "Allow" in the notification window that appears
on the left side of the address bar to receive notifications. Other browsers Allow blocked notifications in your browser’s settings.