Hello @Christophe HAMERLIK !

Welcome to aboard!

Both mentioned problems are known:

1) "the redirect URI provided is missing or does not match" problem means that you missed this step around the installation process (described in this doc https://unacms.com/wiki/installation-overview):

1. UNA Key and Secret

• These are required for updates and app installations
• Obtain them from your UNA account
• If you don't have them, click the "Get UNA Key and Secret" link

2) the 404 error (page not found) means the existence of 2 possible problems:

a) your installed UNA package doesn't have the default .htaccess file in the root (can be taken from here https://github.com/unacms/una/blob/master/.htaccess)

b) your hosting doesn't have the enabled or working modrewrite Apache module. So if the point a is fine then your need to ask your hosting support about it.

BTW - could you please specify which points are missing here:

The installation was not so easy on Debian as the doc is missing few things,