You don't see position Breakfast on your invoice, they summ all cost in one position from one day with VAT 7% and next with VAT 23%, in our invoice I have two mistakes and spend same time at FD to understand what was written on it.

Standard price of breakfast is 75PLN,
If you have voucher 10USD extra payment for breakfast is 30PLN if this breakfast is billed at restaurant and 25PLN if it is told at FD at check-in.

Our stay was divided to two reservations and on first check-in I told that we want breakfast with this voucher 10USD and price was 25PLN, on our second continuing reservation 'virtual' check-in and check-out next morning on breakfast staff told us that we don't have breakfast and we need too pay I sign bill at restaurant and later at FD they told me in this situation breakfast cost 30PLN + voucher per person.