If you have accidentally paid for a voucher twice, follow these steps to rectify the amount (Please note that your cash up will still be out but the voucher will be correct) :
Create a new item from the management site called something like 'Voucher Charge Fix'
Give that item the sale price equivalent to what was credited by mistake to that voucher. Alternatively, make it a miscellaneous priced button where you can enter in the price on the till.
Add this item to your menu & press Save
On the posBoss iPad app, Select Settings > Sync Menu
Select the new item 'Voucher Charge Fix' and add it to a new order.
Charge the order to the voucher that needs the refund
On the Management Site - remove the 'Voucher Charge Fix' from your menu. Press Save
On the posBoss iPad app select Settings > Sync Menu
Make a note for your financial system that explains the variance in your cash up. There is no way currently to reverse the payment itself in posBoss on accounts and vouchers.