Citizens of Chile won’t need a visa if staying for fewer than 90 days.
https://www.vietnamimmigration.org/vietnam-visa-waiver-program/
Accordingly from a notification from Foreign Ministry of Vietnam, from 11 August 2017 Chile ordinary passport are exempted from Vietnam visa requirement.
Requirement : passport must valid for at least 6 months.
Please find below for the agreement between Vietnam and Chile regarding the visa exemption
Agreement On Visa Exemption Vietnam-Chile
Hiep Dinh Mien Thi Thuc Vietnam – Chile