I Played at a rate of 0.5$ per turn in a slot called "Quest West". I caught the bonus game, but after it ended, my winnings were 0$. Tell me, is it possible?
Sounds like a question from a player who just played a slot game for the first time, am I right?
As AnomeBaret said above, bonus round does not give you any guarantee of winning. You may win nothing, you may win small as well as you may win big from the bonus round.
I've tried many slot games and let me tell you that what you have just experienced is a common thing for me as I experienced it many times already.
I understand it very well, as I thought the same as you when I tried slot game for the first time.