Do I need to buy a one-way or round-trip ticket to enter Vietnam?

The conversation discusses the ticket purchasing requirements for applying for a visa to enter Vietnam. It is mentioned that travelers may need to show a return ticket at immigration. Depending on the passport, a visa may also be required, with the application potentially needing return ticket information. Some advice suggests that one can apply using intended flight details without buying a ticket initially, and once the visa is approved, a one-way ticket can be purchased.