THB 400K vs THB 40K route
Route 1: THB 400,000 held in the foreigner's sole Thai account — never a joint account — for 2 months (first) or 3 months (renewal). The balance may drop to no less than THB 200,000 for the 3 months after approval, but must return to THB 400,000 for the remaining year. Route 2: A monthly income letter of THB 40,000 from your embassy; the UK, US and Australia no longer issue these, forcing route 1.