@Declan *********
immigration at the airport won’t ask for funds as you have the DTV granted before arriving ( you will already have had to show funding requirements to get it etc )
But if you choose to extend your initial 180 days whilst still in Thailand - for this you need visit a local ( non airport ) immigration and ask for what’s called an extension of stay ( for another 180 days ) and that’s when you will have to show further supporting documents
The Thai official explains everything about the DTV in this interview
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