Without investing, you can earn money but you will have to trade your time, or resources for it. It is a different revenue-generation model where money won't make more money.
If you can come across a niche and become an expert, you can earn a lot of money. You don't need initial investment. Just take a look at the hourly rate of consultants and lawyers.
Sometimes, it helps to plan and work out a number that you need and work your way backwards. You don't just want to earn money without a clear goal. Also, you have to align your passion with the work you are doing. That way, your earning money won't seem like a chore.