REST API Design Rulebook by Mark Masse
Two huge problems with this book. It's short and very repetitive so the information content is about a couple of blog posts. The 'rules' are highly subjective, and much of the book is pushing the author's WRML 'standard' which I've never seen in the wild. The only real positive is that it's a comprehensive survey of the issues you need to think about when designing a REST API: just don't take the rules as gospel and research best practice from major APIs so you understand the context.