Does working online in Thailand trigger personal income tax for expats?

It's pretty straightforward really. You can work remotely from Thailand without any issue on a DTV. However if you spend 180 days or more inside Thailand in any calendar year then you become a Thai tax resident in that year. You then have to look at any income you bring into Thailand in that year, if that is more than 60k baht then you have to get a TIN (Tax number), more than 120k baht you have to file a tax return. If you've paid tax on that money elsewhere AND where you paid that tax has a dual tax agreement with Thailand then you can claim a credit against Thai tax for tax already paid on the income you bring in

I am also confused about this because I was on Non B and a tax resident here. Then I swapped to DTV , and my previous employer said that if I don't move more then 200K a year to my Thai account I am good, but I would also need to check with some expert if I want to move some of my online company based in HK what's the matter with the tax. I filled this year tax return but I don't know what to do during the rest of the year as it restart.

After 180 days in the Kingdom within a calendar year you become subject to Thai tax law. You will have a Thai tax liability only if you have assessable income. Whether you will actually pay any tax depends on your personal situation.