Thanks for the heads up!

I’m trying to change it but apparently it’s not possible to adjust URLs after submission?

Hoping one of the mods could help with this!

Fixed now. That was a bug in our software - sorry!

Btw, for a Show HN that's a book, the convention is to provide a sample chapter (or something similar) for free. Otherwise there's no way for users to "try it out", which is the necessary condition for a Show HN: https://news.ycombinator.com/showhn.html.

Just added another comment with a link to a sample chapter. Thanks!