In Bangkok, you are going to go to Chaengwattana Immigration office, Government Complex Building B.
And you can book online. If you book online, you need to bring a printout of the appointment and show it to the officer.
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Check this requirements list from Bangkok office, but you still NEED to go to CW to get the latest one.
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As shown in the requirements sheet, You need to have more than 15 days (<- calendar days).
Your funds have to be shown as international transfers in your bank record.