Another way to generate passive income is to invest and be a silent partner in a business. This is very risky, but with risk comes the potential for high returns. For example, several years ago both Lyft and Uber were looking for private investors to invest in their companies. Today, they are worth billions - but you as an investor would only reap that benefit if they go public via an IPO, or get acquired. So, it's risky.
Once you’ve been approved and sent your products to Amazon, simply sit back and allow them to be sold. You never have to deal with fulfillment, shipping or customers service whatsoever. All you need to do is get your products to Amazon and collect your payments. This is mostly passive, but does involve some input of your time along the way once things have been configure.
Residual income is calculated as net income less a charge for the cost of capital. The charge is known as the equity charge and is calculated as the value of equity capital multiplied by the cost of equity or the required rate of return on equity. Given the opportunity cost of equity, a company can have positive net income but negative residual income.