There is work to do, though. Doctors, lawyers, engineering, etc. Lots of work for skilled labor. You can't just "turn on more machines" to placate unemployed unskilled labor.

What if the majority of people can't afford doctors or lawyers?

Then many of the doctors/lawyers burdened with extreme student debt and unable to find work will put pressure on the insurance companies and ultimately charge lower prices. That's likely decades out though.

The machines have owners. How do you make them give away whatever they produce?

They may have to. If there is no money to buy these things, then they'll be back living at home, too.

Don't be naive. Governments and corporations will just devise laws that you HAVE TO buy these goods. How do you muster the money is, and always will be, your problem.

They'll find a way to make money, don't you worry about that at all. They'll sooner make you owe money by the mere fact you're born than to give up.

through legislation, i.e. the recent push toward universal basic income.

personally i think in today's world in which 0.1% owns pretty much everything or at least controls ownership of everything, it's an unavoidable eventuality, but it's not going to be an easy process of getting there.