This can be a little easier said than done, but if you have a large social media following, you can definitely earn money promoting a product or advertising for a company. You can even combine this with different marketing campaigns if you are an influencer and have your own blog (advertisement + affiliate income). This is how many bloggers make money! Again, it is not 100% passive but once set up correctly and then scaled, can be surprisingly lucrative.
Before answering this question, let’s quickly define income: Income is all the money that you earn through any means and streams. There are 2 basic ways to earn money: Passive and active income. Active income is where you sell your time for money - this is your regular everyday jobs. You come into office, sell your time for a certain amount of money per hour, and then at the end of the month you collect your paycheck. Pretty simple and almost everyone understands that concept. However, many don't accept that concept as valid, and see it as slaving off your time instead of putting it to good use and things you actually prefer doing.
PPS oh you thought I was done did you?!  The other parts of the book, although not truly passive income generation focused, are amazing too.  I know things like the low information diet and killing interruptions have made a huge difference to my success – and if I can try and get a little more consistency in my adherence to them, then happy freaking days!