Hi
Also, together with the online application they require
beforehand these documents:
*In order to issue a visa we need:
original passport valid at least 6 months
airline ticket
application form filled on line and stamped
one photo (passport size)
copy of the payment
So, I am afraid that we might need in advance the flight tickets.
Yes, some countries do require plane tickets. For instance PR China, does also and I had to buy one before requesting visa before travelling to Shanghai in 2015. I don't recall if Viet Nam also does, but it should not be an issue.
This means that if you fear that you'll not receive a visa, you can book fully refundable tickets. If you don't get the visa, just cancel the fully refundable tickets and you only lost time and the occasion to attend the conference.
If you get the visa then, if the refundable tickets are more expensive, make a new reservation of non refundable ones and cancel the refundable ones. If the price is not very different, you can enjoy your trip.
But typically the refundable ones are more expensive, so you might need some cash to block in the refundable tickets before you cancel them. Also note that the refund might take some time, so you probably need money enough for both, if you're not willing to wait until the refunded money arrive in your account.
Please feel free to make any comment or suggestion on how do you
think would be the best to proceed with this.
Eddy