Haw. Rev. Stat. § 247-8

The director of taxation may order the refund in whole or in part of any tax which has been erroneously or unjustly paid. The order shall be made in accordance with section 231-23. As to all tax payments for which a refund or credit is not authorized by this section (including, without prejudice to the generality of the foregoing, cases of unconstitutionality), the remedies provided by appeal or by section 40-35 are exclusive.