What does "Double tickets need to be purchased separately for exit" mean? Do I need to buy a ticket again?

The sentence “Two-person tickets need to be purchased separately to leave the park” means that if tourists holding a double-ticket want to enter the park again, they need to purchase additional tickets. In other words, the double ticket is only valid for the first time entering the park. If you want to enter the park again, you need to purchase additional tickets.