I was also rejected the first time in Hanoi and went to the embassy. There is a little counter and someone will come and speak to you and you can ask them the reason and ask them. That’s what I did and then I re applied in Hanoi and was approved
that’s great to hear as I was going to go to Hanoi as well next week to apply…do you have to then go into the embassy to get the stamp after you apply and are approved online ?