Edit site/settings/system.yaml and add the following to your redactor settings
plugins:
- definedlinks
- imagelinks
definedLinks: '/cp/addons/page-links/pages/get'
after adding the settings it should like like that
redactor:
-
name: Standard
settings:
plugins:
- definedlinks
- imagelinks
definedLinks: '/cp/addons/page-links/pages/get'