Do I need to transfer 800,000 baht to a Thai bank before applying for a visa extension?

@John *********

while that is true, as per the law, do remember that the immigration office/officer has the discretion to require further documentation than the law requires as a minimum, if they deem it necessary. Many people have been asked to provide proof of the source of income. Both for banked money and monthly transfers. For most that means providing some pension documents and/or statements from the home country bank.

Normally though, you are absolutely right.