When we first did them ( I own the first muay thai gym to secure a DTV) we were doing 10 private lessons. But it quickly evolved and embassys started asking for a course that matched the length of stay. So we started doing 6 month courses at 1 class a week for 6 months, to match the 180 day stamp and to avoid the embassy issuing a tourist visa instead of a DTV. There are still embassys that accept shorter courses still but it's a gamble. We've done over 60 now with no rejections ( 2 had to re submit though)
we are just a gym not a visa agent we only really know about the muay thai documents. we had about 8 get it at ho chi minh so far but they all had decent bank statements so i have no experience on their minimum requirement. we have found hCM and Jakarta the less drama so far. on our 61st now, only 1 fail (bank statements at vientenne)
Alex is right different embassys have different requirements. There objective is to decide the course is professional and well organized with qualified coaches. Some examples of how they decide this is to ask for Ltd company certification ( registered for tax) , sports authority licens, board of boxing sport A License coach certification, ministry of education instructors certification ( department of skills development)
It's rare to find a gym with all these so to some degree it's like taking a chance.
We are in a fortune position and have all certification but by no means does it mean a gym without all isn't legit .... it's just .... you know... embassy bull s it!