Stock dividends: Some stocks, especially stocks from big corporate standouts, pay dividends to shareholders based on the number of shares they own, and the percentage of the stock price on the dividend date. For example, if a company pays out 3% on a stock that's trading at $100 per share, you'll earn $3 for every share of that stock you own. Add it up and that can be good take-home pay as a passive investment.
If you are not able to get a mortgage on the property, there are still a few options available though rates can be fairly high. You might try approaching the seller for owner financing where they sell the property to you on monthly installments. This might not be possible if there’s a mortgage on the property since many carry a “due on sale” clause. If you do go this route, make absolutely sure you get a notarized contract with all the details.
If you have specialized knowledge in a certain topic, you can put together an online course to teach others. For example, if you have experience in real estate investing, you can create an online course “Real Estate Investing 101”. The benefit of an online course is that once you create the course material, you can sell it to as many people as you want.