On the price list item (voucher), the following settings need to be configured:
Regarding the sale of vouchers, it is sufficient to add the item to an invoice in the standard way and save it (it will be submitted to EET correctly).
Regarding the redemption of a voucher by a customer, the voucher must be added to the invoice with a negative amount (or quantity). The EET message will be sent correctly and automatically — if the quantity is +1, message type 23 will be sent; if the quantity is -1, message type 24 will be sent.