Was wondering same, but I'm guessing they'll be marked as used as soon as promotion ends on 31st May. Although the button 'used' worries me a little, not sure if should tap it?
No joy from support but just read the terms FAQ and found this:- Does my entry still count if my voucher is showing as 'used' in my Samsung Pay account?
Don't worry, your prize draw entry voucher will count as an entry whether it is showing as 'used' or 'unused'.
So I'm guessing it's an automated entry. There's some good prizes on offer and quite a few of them (2000+)