The short answer
FlightVerified has not found a current official Vietnam e-Visa rule that says every applicant must submit an onward ticket. That means the sensible first step is to identify whether you are using an e-Visa, visa exemption or another entry route before arranging any onward reservation.
What the official e-Visa material focuses on
The Vietnam Immigration Department's e-Visa process focuses on passport eligibility, the online application, payment and issuance of the electronic visa. Current official material also states that e-Visas can be issued for single or multiple entry for up to 90 days.
What still needs checking
- Your passport's visa, e-Visa or visa-exemption eligibility.
- The permitted stay and entry/exit dates on the visa or exemption.
- Your airline's boarding-document requirements.
- Whether your next destination requires a visa or other entry permission.
- Whether any onward itinerary remains valid when it may actually be checked.
When to arrange onward evidence
Arrange it when your actual visa, exemption, airline or border context calls for it. Do not treat "proof of onward travel" as a universal Vietnam purchase requirement.
Check Vietnam route