If you cancel your ticket after 24 hours, you will be charged an additional cancellation fee. Passengers with good reasons, such as illness or the loss of a family member, can cancel their tickets without incurring cancellation costs. According to https://www.airtripsadvisor.com/british-airways-cancellation-refund-policy/">British
Airways Cancellation Policy, they must present sufficient paperwork.
If you cancel your tickets within the time frame set by the US Department of Transportation, British Airways will not charge you anything. Domestic flights need a $125 cancellation fee after 24 hours, while international flights need a $450 cancellation cost. If you book tickets with American Airlines, a British Airways business partner, you will not be charged a cancellation fee if you purchase fare add-ons. The cancellation costs are determined by the length of time it takes to cancel a ticket while taking into account the flight's departure schedule.