You could likely earn money posting ads online for companies if you do your research and make sure the company is legit.
But be aware that a lot of those post ads online jobs are scams. So really do your research.
I'm not sure of any legit companies that you can make money posting ads online but I'm sure there's a few out there.
Remember you shouldn't have to pay any fee upfront to get started with those jobs and if they want an upfront payment then it's likely a scam and should be avoided.