I just implemented the payment system on my job board https://www.linuxjobs.fr but it was not yet mandatory to pay to post a job offer. Someone thought it was and paid!

Just the "Wow" moment of my side project :) Of course I switched immediately to enforce it was mandatory from now on to pay to post job offers.

I copy pasted a link from clickbank into some cheap ad. Spent $10, made $300

So the process is you buy an affiliate account from clickbank, then you entered that link into a Facebook ad or what?

I googled "cheap traffic" and by shear luck it got positioned on a relevant forum.