Interesting Book On an Argument for Moral Realism

I haven’t read this book, which was published last year. I’m posting this based solely on the description provided here.
As someone interested in metaethics generally, I think the book looks¬†very interesting. I’m skeptical, however, of the claim that “were it not for the existence of moral facts, we would not be able to perform ordinary speech acts such as promising.” I guess I’ll have to read the book to find out how Terence Cuneo defends that claim.