Hi ComGrafPL,
Thank you for your reply. The point is that we don't want vouchers to work as discounts. We have b2b customers that want to buy vouchers in bulk and use them as gifts for their clients. In order to comply with local regulations, when a customer redeems one of these vouchers, we have to generate an invoice including the real value of products without discounts. That is the reason why the voucher needs to work as a payment method.
It is the same system used by Amazon and big physical big stores when you reedem a gift card.
Regards,