The gym needs to be registered both as a business entity and also a sports entity.
Tiger eye in Bangkok has done loads of these. Just do a search in the group
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If your gym can't provide one then go to a gym you can at least drop into once. This is why a gym in Bangkok will be a good option as almost everyone is going to fly into Bangkok.
Also, tiger eye doesn't force you to sign up for long courses. You have regular options as well
Go the Muay Thai route. Seems the least hassle. Which city are you in? I have a Muay Thai gym in Bangkok that has done many applicants and we're one of the most popular gyms for the DTV. We're called Tiger Eye
I have a Muay Thai gym in Bangkok, and if you are living in Hua Hin it probably makes sense to choose somewhere close to where you live, you might want to look at more options in Hua Hin.
Our gym is called Tiger Eye and feel free to see our reviews in this group.