As reported by the user:
After fresh installation of the plugin, "Configuration step 1", clicking the "Fetch" button redirects to a page that says "Sorry, you are not allowed to access this page.".
Conclusion
The redirect should send the user to:
/wp-admin/network/admin.php?page=gitium%2Fgitium.php
instead it sends them to:
/wp-admin/admin.php?page=gitium%2Fgitium.php.
Screencast
https://cl.ly/e52ccf03dfce