When you cancel a non-refundable ticket, it will only charge you the tax at the time of cancellation.
It’s worth noting that aspirants don’t have to pay anything for cancellations due to emergencies.

https://www.cancellation-polic....y.com/singapore-airl

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Singapore Airlines Cancellation Policy, Cancel Flight Ticket & Refund Policy

Yes, Singapore Airlines does have a 24-hour cancellation policy. According to this policy, all passengers can cancel Singapore airlines flight ticket within 24 hours.