All restaurants have a minimum online cancellation period, and it varies by restaurant. E.g. some restaurants may allow diners to cancel a booking online 1 hour before the booking time others may only allow a diner to cancel a booking online 24 hours before the booking time.
If the “Cancel Booking” button is greyed out, it means the booking is past the restaurant’s cancellation period and can’t be cancelled online. If this happens, you should phone the restaurant directly to advise them of your cancellation. The restaurant’s phone number will be included in the email and/or SMS sent to you.