Although it is technically possible to make a profit while playing online slots, you should not see this as a potential source of income. All slot machines are programmed to make a profit for the casino at the end of the day - not for the player.
While you may experience a long winning streak, this will certainly not continue forever. Therefore, it is important that you view online slots only as a source of entertainment, not as a source of income. You should not gamble with money you can afford to lose.