vouchers are made to be redeemed, and when at a $0 balance, they can be archived. However, there are some circumstances where you might need to remove one that has been paid, such as after expiry.
To do this, you will need to create a new button for your menu.
Set the sales price to be the amount you need to remove, or make it a miscellaneous price button.
Name it something like - "Voucher Expiry"
Add the button to the menu, save.
On the Bustle iPad till app go to Settings > press Sync Menu
Create a new order by adding the "Voucher Expiry" button to it with the correct price needed to bring the voucher back to $0.
Assign the order to the account to get it to a balance on $0.
Archive the Voucher
Remove the button from your menu, delete the item and sync the menu on the iPad app again.