I'm trying to create a pop-up book, using this lesson: https://www.youtube.com/watch?v=I6GjavMTaiQ
But I can't Parent bone that moves the page of the book to the bone that moves the cover of the book - in the setting of the bone, this option is inactive:
I tried the usual parent (Ctrl+P) but in this case, the position of the bone that moves the page, is not recorded in the library of poses, when I move the bone that moves the cover of the book.