yes you can but as many said it's a risk, also make sure you have vietnam visa ready to go back for interview on a day notice...i know personally people applied on there home country while they were in thailand and it worked for them but its a risk so it is up to you.....

there is something called too many documents, Embassies do not care and actually find it to be Red Flag when anyone provide too many extra documents.....also make your documents very clear and straightforward... i have a feeling somewhere in the process the person dealing your application got lost and find the documents confusing... it's not there job to correct... there is no harm to go to embassy and try to talk to them., you can always try to apply again.

@Nick ******

i agreed this is NOT basic requirement otherwise they would have had separate upload folder to receive with the application time like other dox, but they can definitely ask it to provide after the application is submitted, if they didnt ask from the OP then it is not why they rejected the application......something else cause them to drop it

when i arrived i handed over my passport/DTV print out and boarding pass, she was very happy and told me to bring the print out every time on future travel......it's easy for them to just scan from the printout using barcode......as an IT specialist i would never allow any Electronic device close to my computer system for security reason.....

only the flight number with date/time, no need for the booking

you should NOT mentioned Poker or any gambling activity , it's a big time Red flag in thailand and 99% your application will be rejected...you do not need to be in that country to apply but you should NOT be in thailand also while you apply outside....also make sure to be available in a very short time to go for interview physically.....

your letter do not need to say anything except

"working remotely (work from home)"...

in thailand "Short Time / LongTime" is very common, get used to it

other then DTV, your passport and boarding pass....

if you are the legal owner then you will issue both dox to yourself....otherwise whoever is the owner will do so...