I can come up with a plan of action and implement it for you if you need someone to get it done for you. After going to the cashier window I was told I had to sit at my machine and press the help button but after 15 minutes of waiting and flagging down 3 workers meanwhile (none of whom could supposedly help me and none of whom were willing to get anyone who could) I finally had to press the help button on 5 other surrounding games and finally after 10 more minutes someone finally came and then they still had to go get someone else to help me! By then it's WAY TOO LATE to be able to cancel a voucher before someone finds and spends it! For God sake! This place needs to get on the ball and set up some way of reporting, checking on and reissuing lost vouchers in an immediate manner so as to be able to stop thefts before they can have time to happen! I can actually do this for you if you're not well enough equipped to do so for yourself. The problem with that however is that they don't have any consistent way of going about this.
While I realize that if you are careless enough to accidentally loose your voucher or leave it in a machine you deserve what you get, at the same time the casino does have the ability to cancel it and give you your money back.