I suggest applying for the non-o visa from the US showing you have cash equivalent of 800k thb. Once approved, you’ll have 90 days to enter Thailand. Then you’ll have 90 days before doing one year extension of stay. For the non-o, there’s no background check.
Kasikorn didn’t ask me for certificate of residence this morning when I opened account on my non-o retirement visa with lease, but every branch and teller can be different. You might go to a bank or two and ask for requirements.
I applied from LA a few months ago and was not asked for proof of flight. Uploaded 3 months of bank statements in a combined PDF with the other requested docs and was approved in 2 days.
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