Stamping fee is the fee that must be paid directly in cash to the Immigration Officer at Vietnam International Airport to get visa stamped onto your passport. Stamping fee can be paid in USD, VND, or other currencies. but USD is highly recommended to avoid any unbalanced exchange rate.
As of March 2018, the current applicable stamping fee is:
25 USD for 1-month or 3-month single entry visa;
50 USD for multiple entry visa valid for up to 3 months;
95 USD for multiple entry visa valid for up to 6 months;
135 USD for multiple entry visa valid for up to 1 year.
Note: The Stamping Fee must be paid in cash. No credit cards are accepted.