I don’t think the issue is simply “cities have less space, working couples have less money”. Its likely more complicated than that, because nothing really explains why people in India’s vast rural areas would have so few kids.
Kids aren't valued anymore economically. Parents will spend a lot but kids aren't seen as a literal asset but as a sacrifice. Altogether it suggests that at some point if governments want more reproduction they will have to subsidize it more strange as it sounds. It hasn't been a problem in the past from growing poorer undeveloped regions but eventually we could run out of people to uplift economically, leaving even the most xenophilic to have to breed more as immigration numbers wind up low. That scenario probably won't come to pass this century, but potentially the next or later.