Imafan lives in Hawaii, where Fukien tea apparently grows as a weed and is a pest. For you growing one indoors, the possibility of reseeding is moot and I'm sure you would love for your bonsai to get those pretty white flowers.
Bud drop is a sign of some kind of problem/ stress. The tree drops the flower buds to concentrate on surviving. Could be various things stressing it. One possibility is some kind of mite/aphid/ scales. Fukien teas are known as magnets for insects like that. Have you checked your tree very closely? Mites can be nearly invisible. Try shaking your plant gently over a piece of white paper, see if you see any teeny dots.
Otherwise issues would be just good bonsai care. I don't know for sure, but I expect that it needs better light to flower than just to grow leaves. Do you have any supplemental light on it or are you just growing it by a window? What direction does the window face? In the northern hemisphere, days are still very short and it may not be getting enough hours/intensity of sunlight. If by a window, another possibility is that it gets too cold. Winter has finally hit a lot of the US. There can be very cold drafts next to a window. At night when it is cold, put your hand next to the window and see what it feels like. The Fukien tea can survive lower temps, but it does not like temps much below 55 and cold drafts could shock it in to bud drop.
Also, if it is winter where you are, winter houses with heat running have very dry atmosphere. Your tree will probably benefit from a humidity tray and daily misting.
(I don't know where you are. it always helps to tell us where you are located. There are hardly any garden questions , even indoor ones, that can be discussed without regard to location/ climate. )