I started working on a product that a former consulting client needed. I saw potential in the product beyond the first customer and so I started building it.
I had no landing page, no sign up feature, no stripe billing, nothing. I just had an API that they could query and get back some query results. They asked me to invoice them when the results met their acceptance criteria.
It felt great to send the first invoice two weeks ago and the payment finally landing in my account last week.