Yes, visa on arrival is NOT VALID for OVERLAND ENTRY.
The four international airports in Vietnam that you can receive your visa stamp with this approval letter are: Noi Bai airport (Ha Noi city), Tan Son Nhat airport (Ho Chi Minh City city), Cam Ranh airport (Nha Trang city) and Da Nang airport (Da Nang city).
New update : Visa On Arrival now accept at Cat Bi Internation Airport in Hai Phong city, Lien Khuong Internation Airport in Da Lat city.
(*) Note: If you plan to enter Vietnam by land or cruise, please visit a Vietnamese embassy to get your visa or using Vietnam e-visa if you are eligible.
