Visa approval letter is a document issued by The Vietnam Immigration Department that allows foreigners to enter and exit Vietnam in a given period of time. By showing the visa approval letter to Immigration Officers at Vietnam airport, you can pick up your visa and get your visa stamp on your passport upon arrival. Moreover, travelers had better put their correct information into the application form before submitting it since the corresponding authority will verify the details on the approval letter based on your passport and travel documents. If you put wrong your personal details, they will not let you board the plane.
The international airports accepting visa on arrival are Ho Chi Minh airport, Ha Noi airport, Da Nang airport, Cam Ranh airport, Hai Phong airport.