Yeah honestly they don't care if you have an Amazon store just that you have if you're doing the workcation that you have employment that you're authorized to work remotely and that you have income and the amount in your bank to cover the 500K thb
Yeah just write up the letters basically from the position of hte business stating that you are authoritzed to work remotely and that your duties dont involve any work with Thai people or Thai companies and make up an employment contract for yourself