This carrier has a special Singapore Airlines cancellation policy 24 hrs. This policy applies to all flights canceled within the first 24 hours of booking. Accordingly:

During the first 24 hours of the risk-free period of the reservation, there is no charge for rescheduling flights.
These passengers will not be liable to pay any additional charges as penalty.
Passengers who cancel their bookings during the risk-free period will be given a full refund.
This period is calculated from the time of your reservation confirmation.
If you exceed the given time window, you will be subject to payment of required charges.
Generally, this one-day risk-free period policy applies to all types of charges.
This policy is applicable only when your tickets are booked directly on the carrier's site.
Note: Full refunds here refer to 100% refund amount excluding any charges