I have moved the matomo installation from a sub domain to a directory of the main domain.
(System: Ubuntu 20.04 LTS, PHP 8, nginx, Matomo 4.6.2)
Following a new shortend url using the plugin fails (site with the shortcode does not exist) and I get also the following warning:
WARNING: /plugins/ShortcodeTracker/API.php(476): Warning - Trying to access array offset on value of type bool - Matomo 4.6.2 - Please report this message in the Matomo forums: https://forum.matomo.org (Module: ShortcodeTracker, Action: getShortenedPagesReport, In CLI mode: false)
(System: Ubuntu 20.04 LTS, PHP 8, nginx)