Vouchers not working is very rare. Try using incognito/private browsing mode. If still not working Take a photo of your voucher and send a private message to a Moderator_Team, they will help to resolve your problem!
@slick4689 it depends on the browser you're using. Some call it incognito, some private browsing, and I'm sure there are others.
Safari calls it private browsing, Chrome it's Incognito - those are the two I use most.