2 options - book the exact flight with a flexible ticket so you can move the date or book another flight.
I do not think you need to book the exact flight but you do need to show you are arriving before your course starts - this is probably what they want evidence for since itβs very soon
2. Do you have a non-b visa now? If it has already expired you will be fine.
3. Utility bill, bank statement or similar worked for me.
Other documents for me was additional proof of employment - letter from employer, also they wanted to see my boarding pass out of Thailand and my exit stamp.
I think the main thing is ensuring you can support your stay and you are actually in the country you are applying from.
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