Problem
A dockerized app (f.e. rocketchat) can not be installed.
Environment
UCS 4.4-4
dockerized app
Solution
If you had installed a dockered App in the past and removed it, it may happen that data of the old installation resists on the system. In our example we check:
root@ucs:~ # ls -l /var/lib/univention-appcenter/apps/rocketchat/
and we remove the old data:
rm /var/lib/univention-appcenter/apps/rocketchat/