There is quite a simple way on how to make money on twitter, the only thing you need is followers and an affiliate program.
What's an affiliate program? Well it's basically a form of advertisiment, where you link a product and if someone clicks on your link and buys the products, you get a part of money.
Okay, so first of all you find yourself a niche, in which you will operate. You then need to get followers - at the start you need to do the follow for follow method and then you just passively gain followers, of course there needs to be some engagement from your side. Lots of relevant posts and reposts. Also there are lots of free twitter tools, which you can utilize.
After you get a bunch of followers - you sign for an affiliate program related to your niche (cosmetics, fitness, food, gaming, ...) and if you get accepted by the company you can start making money.
Then you just do everything in a loop, you get followers, you get more potential customers, the more customers, the more money.
Thank you for sharing this informative post with us. It is my opinion that these affiliate programs are potentially really great. But I do have the feeling that sometimes it comes across as kind of a multi level marketing / product placement thing. And with that I have a much more negative feeling. So the way these networks operate is truly important. Have fun out there and good luck with your future posts!
Oh yeah, I agree, the plus of this method is that you don't need any investment (except a bit of your time, like 20 minutes daily I'd say)