I didn't realize that instant booking was 'on'. Someone requested to stay and I sent them a note stating that the room wasn't available. I am being charged 50 dollars. The booking would have been for 15.
@Margaret556 they requested or they booked? If you canceled a booking then yes you will be charged and not only that, you calendar will be blocked. Why wasn't the room available? You are responsible for keeping the calendar up to date. If it was some extenuating circumstance you should call Airbnb and explain, maybe you won't need to pay.