According to United Airlines' 24 Hour Cancellation Policy, passengers who cancel their tickets within the allotted period do not have to pay a cancellation charge. If you cancel your flight on the same day as your reservation, the airline is required to provide you a full refund. Within three weeks, the whole refund will be transmitted to the original mode of payment.
United Airlines has a 24-hour flexible booking window, which means that if you cancel or amend your ticket within 24 hours of your scheduled departure time, you will receive a full refund in your original payment mode, less any cancellation fees. Passengers must pay a cancellation charge after the 24 hour booking period has expired, according to United Airlines 24 Hour Cancellation Policy