Thanks for your question!
It is informed that you can apply online on our website for visa on arrival but we JUST can help you to process 1 month single tourist visa and the service fee is $120US/person (not including $25US stamping fee at Vietnam airport). However, the Vietnam Immigration does not process 1 month visa for full 30 days, they just bases on your ticket to process visa. The processing will take 7 – 10 working days
And you can apply online at this link: https://www.vietnam-evisa.org/apply-visa.html
In addition, after finishing payment online, please send us your passport scan + hotel booking + return ticket via email. Without those documents, we can not process visa for you
If you want to stay longer, please go to the Vietnam Embassy to apply visa
In addition, EVISA is not availble for Sir Lankan citizens