Visa Laos - Vietnam

A friend and I are currently trying to sort out a visa for Vietnam. We  want a 3 month multiple entry visa. We are not flying into Vietnam we  are currently in Muang Khua in Laos and were hoping to get the bus  through the 

Sop Hun / Tay Trang borders.

 We have already purchased a visa but the approval letter states the  airport on arrival as Ha Noi. Can we still use this approval letter at  the border we are trying? Or will it be rejected? Every Visa we have tried to apply for online has asked us to state an airport we’re flying into. 

 Please help! thanks, Ollie.