If you offer vouchers to redeem, we recommend that you create two products in the administration with a positive and a negative amount. For example, a voucher worth CZK 500 and CZK -500. As soon as you sell the voucher to the client, you mark the product with a positive CZK 500. When applying for a voucher, you choose a minus product of CZK -500, which deducts this amount from the final amount.