Thanks for your questions.
In this case, we would like to recommend you to apply for 3 months multiple entries Visa. So you are able to use this Visa to enter Vietnam many times within 3 months.
The service fee for this Visa type is 35USD, then when you arrive Vietnam airport you pay more 50USD for stamping fee to get the Visa stamp.
Firstly, please fill in the application form online on our website here https://www.vietnam-evisa.org/apply-visa.html, within 2 working days, you will receive the Visa approval letter via email. This Visa letter is issued by The Vietnamese Immigration Department, so we guarantee 100% that you are able to enter Vietnam without an issue.
For any question, please contact us via email firstname.lastname@example.org or call us at: (+84) 909 343 525