When using the FP app to cancel on a latitude FP within 24 hours of booking, I've had it intermittently prompt for credit card to complete the cancellation, while website performs cancellation free of charge as expected. This happens for departures under 24hrs out as well as beyond multiple days out. If the OP was on latitude (doubtful given the question, but not explicitly clear) the app might give the wrong impression wrt cancellation. Have not had a flex pass for years so cannot compare.