What should I do if my DTV application at the Embassy in Hanoi was flagged for insufficient funds?

On most Thai embassy sites they state exactly how much you need to show in either the local currency, or a currency they specify. When I was helping someone from the UK apply in Vietnam, the amount we used was over the ฿500,000 and we added a note showing the current exchange rate from GBP to baht on that day as we couldn’t expect Thai staff in a Vietnamese embassy to know the exchange rates for a multitude of currencies.

You cant go to the embassy or consulate. Everything is online.

They’ve clearly stated ‘not enough money’ so you’re going to need more.

Try to make it more than ฿500.001

So they didn't reject you then? Seems like they're just seeing if you had quick access to other cash to top up the account.

It all depends on the conversion rate they are using. They might actually not be converting UK pound into Bhat but UK pound into Vietnamese Dong

Today's exchange rate is 43.5 baht to the pound so £11,000 is less than 500k baht. I don't know what rate the embassy uses but it could be a lower rate than this

Actually, £11,500 is juuust over the 500,000, and a random currency fluctuation could take it below. Attach a currency conversion from google with your bank statements as well.