I think I’ve found your problem.
Your reviews are great. The endorsements are fantastic.
I’ve sold over 250,000 self-published books on Amazon and as many traditionally published. However I’ve never paid more than $1,000 to promote a book.
Buying ads is a way to bring readers to a book that is getting ignored, but in my experience it’s not going to drive sales. Every book is different. I’ve serialized them in podcasts, spent day-after-day livestreaming and done everything else I could think of.
If I had to guess why it hasn’t been getting traction it might partially be the page count. 138 pages for an ebook feels steep to me. I’d also keep playing with the description. That is extremely key. I had one novel go from well-reviewed but modest-selling to a 100,000 in sales (and getting me in an Amazon press release as one of the top 10 selling indie authors that year) after I changed my cover and description to better represent the book.
Side note: The title sounds a lot like Guy Kawasaki’s Art of the Start and may confuse people. I’d hate for what sounds like a wonderful book to get looked over.