So I just went through this whole thing last week trying to find 'Fat Keily' myself. From what I could dig up, it's not free anywhere officially, at least not currently. The author has it listed for purchase on Amazon Kindle and Kobo, but I didn't see a free version on those major storefronts. Sometimes you'll find a free sample, but that's only a chapter or two.
I did check a few of the library apps like Libby and Hoopla, since libraries sometimes get ebook licenses, but my library system didn't have it. Might be worth checking yours directly, though, because collections vary so much from one county to another. Might have better luck in a bigger city system.
Ended up just using a Kindle credit I had. Wasn't willing to wait around hoping it'd pop up for free, and honestly, the price was fair for the length.