Are you applying from the US?. From my experience, there's low chance they'll provide you medical plan prior to you, seeing doctors and be diagnosed in person. I applied for DTV for my bf here in the US. We submitted an invitation letter from the hospital along with his past medical records from hospital here to back it up. We got approved within 7 working days. I recommend writing a letter stating why you find Thailand as your healthcare destination, let them know your genuine intentions, then you'll be fine.
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