@Ron *****************
, Three ways to show the proof of 40K baht a month income if you are using that method
1 - If your embassy issues the income affidavit notary letter you must use that
2 - work legally inside thailand (with a work permit) and show proof your salary is at least 40K baht a month
OR
3 - transfer from abroad into a thai bank account in your name only a minimum of 40K baht a month, each month, every month for the previous 12 months before you apply for an extension