Ghostwriting stands as one of the best ways to make money by writing online. You will have to forfeit your rights to your written work, but you also make sure shot money. You can of course publish on Amazon and make money but generating sales is really hard, but with ghostwriting you make guaranteed income. Do you ghostwrite? Where do you get ghostwriting contracts?
Your best bet would probably either be Upwork or Fiverr. I've never done ghost writing, but I imagine both sites have such options. Though I would imagine there are a lot of people doing the same work, so keep that in mind.
That's right, freelancing platforms like Fiverr and Upwork are the best places to find ghostwriting opportunities, I have done a lot of ghostwriting jobs through Upwork. Some of my ghostwriting assignments fetched me as much as $600. These days I am not active on upwork and I am trying to look for ghostwriting opportunities through forums.