You are mixing COE and Visa’s up. Check on the thai embassy’s website which visa you’d like (which will depend on your length of stay); then apply the visa (or go for visa-exempt route) and after you have done that, apply for the COE
i have been through the process. I am in ASQ right now. I give advice the way I see fit. The person seemed confused about what the message meant. Maybe you should stop being so condescending.