I really don't think we do know how to stop it. Even massively increasing welfare payments has totally failed to produce lasting change where attempted.

It is possible going significantly higher could, but if so we have not yet figured out how high, and it's clear the threshold is much higher than people have tended to think it would be. E.g. look at financial incentives in Hungary, or the welfare system in places like Norway that makes parental leave in many developed countries look like third world conditions.

Rich people do seem to have a somewhat higher fertility rate, so it is possible that you could fund it enough, but the rise happens at high enough income levels I don't think our economy could handle it.

I agree with the rest of your comment, though - I just don't think we know if purely financial motivation would be sufficient at a level that is actually possible (and I do fear authoritarian approaches will end up being tried instead). It might take a lot more effort than that in terms of lightening the burden and/or making it more attractive in other ways.