Working smart is applying the simplest ways to earn huge income while doing it in a less effort like you just only working for 3-5 hours but the return is 10x compared to working very hard but the salary is not big enough to the services that you rendered, but I think you need to combine these two to make your life easier work hard in a smart way.
It doesn't come down just to earning huge income while getting there with less effort. Rather, as I come to think of it, working smart can be conceptualized as achieving some desired outcome doing nothing altogether in the limit, likely even as an off-target effect of a series of other off-target effects. On the other hand, working hard is the opposite of working smart (which is kinda obvious, huh), and in the limit means doing everything and still getting nothing. To me, this is where lies the great divide between working smart versus working hard.