Uploaded book disappeared on Books app

I've been listening to an audiobook I uploaded to the "Books" app. I'm about 40 chapters in, and I opened the book and I got a message that says, "Item Not Available". Subtext says, "The item you've requested isn't currently available in the store for your country or region." But I didn't buy this from Apple because I didn't want to be bound to their mediocre app. I uploaded this after buying it directly from the Author's site. So what is the deal? How can I get my book to show up again without having to find my credentials, redownload, and then reupload the book?