cannot use-package which-key

[Luca Ferrari]

Hi all
,I'm running emacs 27.2 compiled on Linux Fedora 33. If I install
which-key by means of package-install everything works fine, but if I
try to automatically get it installed from my configuration file, it
fails.
My configuration looks like:

(use-package which-key
  :init (which-key-mode)
  :diminish which-key-mode
  :config
  (setq which-key-idle-delay 0.3))


and the --debug-init gives me:

Debugger entered--Lisp error: (void-function which-key-mode)
  (which-key-mode)
  (condition-case err (which-key-mode) ((debug error) (funcall
use-package--warning2 :init err)))
  (progn (condition-case err (which-key-mode) ((debug error) (funcall
use-package--warning2 :init err))) (let ((now (current-time)))
(message "%s.$
  (condition-case err (progn (condition-case err (which-key-mode)
((debug error) (funcall use-package--warning2 :init err))) (let ((now
(current-t$
  eval-buffer(#<buffer  *load*-377393> nil
"/home/luca/.emacs.d/emacs.el" nil t)  ; Reading at buffer position
996
  load-with-code-conversion("/home/luca/.emacs.d/emacs.el"
"/home/luca/.emacs.d/emacs.el" nil nil)
  load("/home/luca/.emacs.d/emacs.el" nil nil t)
  load-file("/home/luca/.emacs.d/emacs.el")
  org-babel-load-file("/home/luca/.emacs.d/emacs.org")
  eval-buffer(#<buffer  *load*> nil "/home/luca/.emacs.d/init.el" nil
t)  ; Reading at buffer position 391
  load-with-code-conversion("/home/luca/.emacs.d/init.el"
"/home/luca/.emacs.d/init.el" t t)
  load("/home/luca/.emacs.d/init" noerror nomessage)
  startup--load-user-init-file(#f(compiled-function () #<bytecode
0x6107c5>) #f(compiled-function () #<bytecode 0x60640d>) t)
  command-line()
  normal-top-level()


What am I missing here?

Thanks,
Luca