Plus, you'll earn an extra mile for purchases made directly with Hawaiian Airlines, with the exception
of duty free purchases made in flight.
From the terms and conditions: «Airline tickets, upgrades, mileage points purchases, mileage points transfer fees, gift cards,
duty free purchases, and award tickets are not deemed to be incidental fees.»
The terms state that «Airline tickets, upgrades, mileage points purchases, mileage points transfer fees, gift cards,
duty free purchases, and award tickets are not deemed to be incidental fees» but there are always exceptions.
Unfortunately airline tickets, upgrades, mileage purchases, gift cards, and
duty free purchases aren't reimbursable, though some people have had luck with some gift cards.