Please note that even though there is no direct law against online casinos in Thailand, they are still considered to be prohibited by the government officials. So, do not get involved in any kind of gambling activity other than the legal ones to be safe.
You just have to stick to legal, regulated online casino sites such as BetMGM, Caesars Palace Online Casino, FanDuel, Betway, bet365 and BetRivers. They offer great casino game ranges and they will pay out quickly and without any issues if you win.