Visa on Arrival
Eligibility is passport-specific, not simply “28 countries”
ICA's current Visa-on-Arrival page lists eligible countries and territories including Canada, Indonesia, Japan, Singapore, the United Kingdom, Fiji, Solomon Islands, Vanuatu and several Pacific territories.
Some nationalities have passport-type restrictions. For example, the current ICA page lists China only for Diplomatic, Official and Service passports.
ICA also explicitly says that mainland New Zealand, mainland France and the United States are not eligible for Visa on Arrival.