This consulate is the one I'm talking about
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you have to be IN Lao to apply, you upload your Lao visa and entry stamp when you apply to show you're there and then you have to GO to the consulate to pay for the visa in person (in CASH 10k baht).
BUT
Right now they are the fastest in S/E Asia..
Someone applied for a Non-B the other day right as they crossed the border and were able to upload their arrival stamps, they went to the consulate between 9-11 that morning and paid for the visa (2000baht) and before they even got to their hotel they had the email saying they were approved 😮
Granted that was a non-B not a DTV, but i think if your documents are good (which they would be seeing as you're getting a piggy back DTV for a spouse OFF your DTV) you should get it approved quickly