A Vietnam Visa approval letter is a document issued by the Vietnam Immigration Department. It is a permit that allows you to enter Vietnam and get a visa stamped onto the passport upon arrival at Vietnam airport, after which you can leave and enter Vietnam for a specific period of time.
It should be noted that the Immigration Department will check your information in detail and strictly before issuing the approval letter, so you can confidently arrive at Vietnam’s international airports when you have this document.
To get the approval letter, you need to apply online through a travel agency licensed to provide visa services, then they will work with the Immigration Department to get the dispatch and send it to you through email.
One note is that the visa approval letter may have the names of some people who are applying for visas at the same time as you.