My wife and I were traveling to see her family and I had just gotten a new IPAD Gen2. All I wanted to do was draw characters on it. My wife suggested I make a book with the simple characters. I accepted her challenge and made a black and white child’s book during our 2 hour flight. In my opinion and hers it was a decent first draft of a story and cute pictures to go along. I was a few months later I decided to finish the project and make it an e-book for sale. Little did I know that process would be 10x longer that the idea and draft part. After a little research I chose to use Apple’s ebook store to post. So I gathered the requirements to post there from around the web. The file format used was .epub. Let me tell you… getting the formatting of the file to be as expected took a lot of tweaking and hair pulling. :D. The next Issue was that in order to post a product on the apple store you have/had to use the mac os. the only thing apple I owned was the ipad I had just gotten a few months prior. I was not about to spend $1000 + on a mac system just to upload this book. So I did what any tech savvy deal loving guy would do.. I dual booted my old laptop with a free version of mac os and pain stakingly got the job done.
https://books.apple.com/us/book/big-scary-monster/id791431884?ls=1
Soon the cash was rolling in and I was able to quit my day job… oh wait…. I had a few friends purchase it and that was about it. the revenue payout threshold was never hit so I have still to this day yet received any $$ from this venture.. My low effort 3D modeled class projects that I posted on Turbosquid have turned infinitely more money than this nice Childs book.
https://www.turbosquid.com/Search/Artists/ColbyDaneSaddoris

It has been years since I made that first eBook. I have since made a second and third book and let me tell you Adobe has a system ( Adobe Express ) that pretty much streamlined the process and turned the making of the third one into an enjoyable memory.