As others have said you have to pay in cash at the airport. You can also pre-pay in cash at the Westpac bank in Avarua. You can also pay on credit card there, but beware. If you do this it will be classed as a cash advance on your card and your charges would be horrendous.

Everyone keeps telling them to include the tax in the airfares - they are foolish not to do so as it causes so much bad publicity. When these charges are included in the airfare no-one bats an eyelid.