> The actual meaning is in my opinion that at some point, when you can pay your bills easily and do not need to worry about money every day, increasing your income doesn't make you happier.

That’s not actually true though. There’s pretty robust research to show that happiness is correlated with log money. It’s not a function that becomes flat after a certain point, at least not as far as any research I’ve read says. Although the correlation or causation question remains: do happier people make more money, or does more money make people happier, or is there some underlying third variable that affects both? But the fact that lottery winners do end up becoming happier suggests that there is a causal element in the money->happiness direction.