@Wendy2065
Somebody has to pay for the reservation.
There is no such thing as a "free reservation"
A Giftcard can be used as a present and can be used by a guest to pay for a reservation.
https://www.airbnb.com/help/article/3616
But this is not your goal.
Alternativily you can offer the nights for a minimum price (I think it is $10,-) and even refund the money afterwards.
Guests maybe still pay some taxes or Service fee.