Starting with version 4.0 SubSpace Navigation for Confluence is compatible with Confluence 9.x only. See Atlassian's documentation about Confluence 9 for more details especially its breaking changes.
Introduction
On the following pages, you can find a complete documentation for this SubSpace Navigation for Confluence release.
The User's Guideis for project managers, developers, and testers – anyone who uses the app.
The Administrator's Guide is intended for Confluence administrators. It helps you to install the app and to configure the SubSpace Navigation.