I have an aunt who's been successful selling online. She even received some household items for free because companies were interested in collaborating with her, so they gave them away, and the rewards had to be advertised as attractively as possible.
Is that affiliate marketing? I've heard it does pay well. You just need a number of followers who always watch you then you promote items in your videos that are being sent to you.
Funding is crucial, because starting an online business requires capital, but it's likely not as large as starting a brick-and-mortar business like a brick-and-mortar store.
The challenge in having an online business is marketing. Since you have no physical store, you have to make extra effort in promoting your business. You'll need connection and social media presence to spread your business. With poor marketing, your online business will not succeed in the long run.