Sometimes I wonder if it's the money per se, or what brings in the money, or both. My guess is the higher-paying jobs are more interesting and fulfilling; conversely if two people have equally stressful jobs, but one pays a lot and the other little, the high pay would mitigate against the stress ("this has these costs but at least it pays well").

This sounds obvious maybe but it's a bit different from money per se bringing happiness. It would be more about the perception of the work.

I also am not sure what to make of life satisfaction as a happiness indicator. It's a single item reflecting one aspect of happiness; there's other components of well-being. The author acknowledges this but it feels like a critical issue.