When you apply for a O or OAVisa the first time, you need to show you have minimum 800 000 Thai bath in a bank at home. In one year you ask an extension, you have to show
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bath came in every month, first extension, you show 3 or 4 months (the most recent months) it's OK in Pattaya, after that 12 months. Avoid Bangkok Bank.
You need an affidavit from the last 3 months pension and a specific letter from the bank confirming 12 monthly payments of a minimum of 65k. That's in Pattaya.