If the open textbook you are working on is a new creation, it will be released with a CC-BY 4.0 International license.
The Project Manager you are working with will add a page called “About the Book” to the Front Matter of your final work. It will include the following sentence about licensing:
Information about licensing is added, by the Project Manager, to the book information section of PressBooks. This information appears at the bottom of each web page of the online version.