At Ho Chi Minh City (Tan Son Nhat International Airport) the VOA window is situated over to the left as you enter the immigration hall, at the far end. Do not join any queue for Immigration Control. The counter itself is sign-posted - "LANDING VISA".  When you get to the Landing Visa (VOA) window, be prepared to hand over your passport, ONE completed copy of Form N1, the entire letter of approval and ONE passport size photo (the officer will staple your photo to the form if not already attached). You should then go and sit down. Even with few people being processed, do not expect passports (with the visa attached) to be returned in the order that they were presented at the window.