reservation ticket; reservation voucher
A physical or digital slip that confirms a reservation, such as for a hotel, event, or transportation.
Please show your hotel reservation voucher at the front desk.
Don't forget to bring your concert reservation ticket.
チケット is a general ticket for admission or travel, not necessarily tied to a reservation. 予約券 specifically indicates a reservation-based ticket.
Compound of 予約 (reservation) + 券 (ticket, voucher).