Maybe start with python, either Django REST framework or FastAPI, and make a todo app. Start somewhere writing your own API and learn what the backend feels like, then when you work with other people’s API you’ll get what’s probably happening behind the scenes and know how to read between the lines with the incomplete documentation.
I’d also say take a look at GraphQL, that is another popular paradigm that’s related.
Gabe Newell, the founder of Valve (Steam) had this to say
“Piracy is almost always a service problem and not a pricing problem”
So many people are willing to pay if it’s a good experience. But if the experience sucks, people with money will find a better service, which in many cases ends up being free. If I wanted to have ads dumped everywhere while I watch videos, there are services that offer that “experience” for free.