Hello,

No, you had (services …) inside (operating-system …).  E.g. a line 47 in
https://git.savannah.gnu.org/cgit/guix.git/tree/gnu/system/examples/bare-bones.tmpl?h=master#n47

Gnu Röoty <walidslack@gmail.com> writes:

[…]

Should be like this:
--8<---------------cut here---------------start------------->8---
(use-modules (gnu) (gnu system nss))
(use-service-modules desktop networking dbus cups)
(use-package-modules certs mate wicd glib cups)
(operating-system
  (host-name "x200")
  (timezone "Europe/Paris")
  (locale "fr_FR.utf8")
  ;; Other configuration …
  (services (cons* (mate-desktop-service)
                   (service cups-service-type
                            (cups-configuration
                             (web-interface? #t)
                             (extensions
                              (list cups-filters htplip))))
                   %desktop-services))
  ;; Other configuration …
)
--8<---------------cut here---------------end--------------->8---

Oleg.