I’m the app creator. It’s definitely not simple but it’s also easier than what most people think. Pretty much anyone on Hacker News could do the same given enough time and motivation. The problem is that it takes a long time to see success. You can easily spend years earning close to nothing. I love doing it but there are definitely pros and cons.

Honestly my idea was not particularly amazing. I was just frustrated with courses that were too focused on grammar and decided to create a solution to this problem. You don’t need an amazing idea, you just need to offer a solution enough people will be happy to pay for :).