It does not require minimal investment. You just have to promote the products of different brands by creating your affiliate links.
Blogging is another great platform for earnings. You have to pick up a niche and write an article relevant to that. You can earn a handsome income through the blogging.
An ebook is a good source for delivering information and value to the readers. You can promote your courses or content to your customers.
If you have the potential to click some unique and trending photos then you can sell a single image to a thousand people by registering a license for that photo.
You can generate income by selling digital products through your YouTube channel. Digital products have good profit margins.