A juvenile Lampropelma violaceopes looks exactly like this one, they are less vibrant when they are young. But yours is not arboreal, it's not Lampropelma violaceopes then... There are very few blue Asian terrestrial Ts, and very few Asian Ts reach only a 3.5" LS as adults. Really hard to tell, do you know if it's a WC spider? Surat thani phang nga has not yet established in this hobby and much darker than this one
Im guessing it is a wild caught spider as it does not have a positive ID. If its wild caught could it possibly be C.paganus? (even though the original specimen is MIA) Deffinitely not hainanum, hainanum are a very large robust Sp. And do not have any blue.