With 0 investment is working online. For example in upwork. You don’t need to pay for anything.
I also give advice on how to search for better jobs and how to use upwork on a series of videos.
Another way is selling Amazon products. In that case, is not 0 investment but only the domain and the hosting (maybe 10 u$s the first year). The idea is to find a niche with a big volume of searches but low competence, and then publish articles on it and sell Amazon products.
I began getting 20 u$s / month in the first month. I find various errors on my site. I think I could be getting 40 o 70 u$s a month. Then making 10 sites as that you can get 1000 u$s per month.
Amazon is not the best paying but I think is the simplest way for the first passive income.
The videos about upwork are:
The video about passive income (in near future it will be with English Captions)
The site I’ve created that gives me 20 u$s each month