Approval letter for exit gate?

[Ozic]

Vietnam visa approval letter help me to get visa at airport. What then? I plan to go to Cambodia through Chua Doc border gate (by speed boat), is there any problem?

[Galent]

Visa approval letter helps you to get Vietnam visa on arrival. After getting visa, the letter is invalid. The visa allows you to stay in Vietnam within the given period. You have to exit Vietnam by the valid date, by land, air or any border gate.