@Max ************
you are giving bad advice if the income isnt covered under the DTA in thailand you are subject to their tax structure
Thailand Income Tax for Foreigners in Thailand | Siam Legal International
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If you are in thaialnd for a accumlitive of 180 days ( doesnt have to be consecutive ) you are subject to their tax no matter if you derive income locally in thailand or from foreign sources. Again thats if its not covered under the DTA