Bouncer plug-in problem

Kirby 3
1

hello,

started a new plainkit. first action was to create a role ‘teacher’, which i want to restrict to page ‘kategorien’ and subpages. created

-kategorien
          -kat a
               -sub a
          -kat b
               -sub b

installed bouncer plug-in
config.php

<?php

return [
    'sylvainjule.bouncer.list' => [
        'teacher' => [
            'fieldname' => 'canaccess'
        ]
    ]
];

and teacher.yml

title: Teacher
permissions:
  access:
    panel: true
    site: true
    settings: false
    languages: false
    users: false
  user:
    changeRole: false
    delete: false
    update: false
fields:
  canaccess:
    label: "Zugriff:"
    type: pages
    multiple: false
    options:
      type: query
      query: kirby.page('kategorien').children

in the canaccess field no selection is shown.
yml indentation is correct.
also tried e.g. site.pages, site.find(“kategorien”), site.find(“kategorien”).children… nothing works.

tnx for any hint…
fusi