I'm trying to provide a discount on a training registration. I see that I can't put a negative dollar amount in for PayPal to calculate it. In my case the event is $80 per day but if a participant attends all three days it's $ 200 for a $40 discount.
One way to do it is to provide your choice of one, two, or three days in a choice field, and then set each one of the choices as a payment field. You will need to set the amount manually in payment field / price / fixed.