Redeeming gift vouchers across stores

At each store, create a payment type called 'Gift Voucher from xxx' (where xxx stands for the store name). Set the banking type to non applicable.

When a customer is redeeming a gift voucher issued from the other store, make the sale (at this store) as per normal and use the payment type of 'Gift Voucher from xxx'

Then on the original stores system (the store where the gift voucher was made), go to Sales Menu > Gift Vouchers. Then search for an active gift voucher and you will see an option in blue that says "Expire." If you click on this it will expire that gift voucher, without refunding the payment made towards it. 

So this in effect uses up the gift voucher, ensuring it cannot be used twice.

(Please note, you cannot reverse a manual expiration so make sure you are expiring the correct gift voucher when using this feature.)