What if I change my flight and arrive at another airport in Vietnam?

Visa on arrival works at any of following international airports in Vietnam: Tan Son Nhat (in Ho Chi Minh City); Noi Bai (in Hanoi) Da Nang (in Da Nang City), Cam Ranh (in Nha Trang), Phu Quoc in Phu Quoc Island. There is no problem with switching between these airports.