@John ********
you need the financial proof for every annual application to the 1-year extension. Since your embassy doesn't issue any income affidavits, you can use the 12-months of accumulated transfers of a minimum of 65,000 THB into your bank account, month for month, not missing out one single month, as financial proof. Noteworthy: these transfers must be coded in your bankbook FET or FTT - as having come from abroad. WISE transfers recently need a special process (through the Kasikorn bank). If you have to switch to SWIFT direct transfers from your home bank to your Thai bank account, it will be a bit costly, however doable.