The Web Booking Portal will ask you for a permission to use Background sync. This is necessary to reflect real-time data without having you refreshing the page manually.
When "Ok" is clicked on the notification, a permission request should appear in the browser:
As soon as a response option is chosen, the notification message at the bottom of the screen will disappear.
I keep getting asked for permission
Any and all website-related permissions are stored locally on your device. If local permissions data is cleared at any point, the permission request will pop up again.
Notification doesn't disappear
If notifications are automatically blocked (disallowed), then the message will not disappear - the website is waiting for a response. There should be some kind of a bell icon near the address bar where permissions information can be view if that is the case:
I want to change the permissions
Website-specific permissions can be viewed and changed in the browser settings (usually under site-specific settings).