Dear LeoKing Seior,
Thank you for your question!
We are sorry to inform that at present our company just provide Vietnam visa on arrrival for those who travel to Vietnam by air. In your case, you enter Vietnam by land, we recommend you to come directly to the nearest Vietnam Embassy in your country or in Phnom Penh to get a visa to Vietnam there.
You need to take your passport, a passport-sized photo, and cash in person . You must also pay the stamping fee and wait 5-7 working days to get the visa. Please note that the application procedures and fees may vary among countries and embassies/consulates.
We do hope that this information is clear and helpful for you.