https://en.wikipedia.org/wiki/Income_and_fertility#Contrary_...

https://ifstudies.org/blog/more-money-more-babies-whats-the-...

https://www.demographic-research.org/articles/volume/51/26

https://www.sas.upenn.edu/~jesusfv/Slides_London.pdf

(your paper is five years old, and is lagging broad, rapid global fertility decline trends; it's not income-fertility, its "educated, empowered women with access to birth control have less kids, no kids, and/or delay childbirth" regardless of income, with the caveat being some higher income cohorts and ultra orthodox religions/cultures [Israel] having higher than baseline fertility)