Hi Andreas,
now I have more severe probs, because it no longer works at all.
When I want to use the etherpad activity or createone I get this error:

So I re-installed the plugin and the errors remains. When I restart the
server I get on the console:
myetherpaduser@ourcompany:~/ETHERPAD/etherpad-lite$ ./bin/run.sh
Ensure that all dependencies are up to date... If this is the first time you have run Etherpad please be patient.
npm WARN prepare removing existing node_modules/ before installation
> wd@1.12.1 install /home/myetherpaduser/ETHERPAD/etherpad-lite/src/node_modules/wd
> node scripts/build-browser-scripts
added 1125 packages in 15.823s
Clearing minified cache...
Starting Etherpad...
All relative paths will be interpreted relative to the identified Etherpad base dir: /home/myetherpaduser/ETHERPAD/etherpad-lite
Random string used for versioning assets: 393f4bd3
[2020-10-07 14:00:05.877] [DEBUG] AbsolutePaths - Relative path "settings.json" can be rewritten to "/home/myetherpaduser/ETHERPAD/etherpad-lite/settings.json"
[2020-10-07 14:00:05.882] [DEBUG] AbsolutePaths - Relative path "credentials.json" can be rewritten to "/home/myetherpaduser/ETHERPAD/etherpad-lite/credentials.json"
settings loaded from: /home/myetherpaduser/ETHERPAD/etherpad-lite/settings.json
No credentials file found in /home/myetherpaduser/ETHERPAD/etherpad-lite/credentials.json. Ignoring.
[2020-10-07 14:00:05.897] [INFO] console - Using skin "colibris" in dir: /home/myetherpaduser/ETHERPAD/etherpad-lite/src/static/skins/colibris
[2020-10-07 14:00:05.906] [INFO] console - Session key loaded from: /home/myetherpaduser/ETHERPAD/etherpad-lite/SESSIONKEY.txt
[2020-10-07 14:00:08.103] [INFO] APIHandler - Api key file read from: "/home/myetherpaduser/ETHERPAD/etherpad-lite/APIKEY.txt"
[2020-10-07 14:00:08.471] [INFO] console - Installed plugins:
[2020-10-07 14:00:08.483] [INFO] console - Report bugs at
https://github.com/ether/etherpad-lite/issues
[2020-10-07 14:00:08.490] [WARN] console - Can't get
git version for server header
ENOENT: no such file or directory, open '/home/myetherpaduser/ETHERPAD/etherpad-lite/.git/37488fa93a0159c141e1ce7df7691241f63'
[2020-10-07 14:00:08.492] [WARN] console - Can't get git version for server header
ENOENT: no such file or directory, open '/home/myetherpaduser/ETHERPAD/etherpad-lite/.git/37488fa93a0159c141e1ce7df7691241f63'
[2020-10-07 14:00:08.493] [INFO] console - Your Etherpad version is 1.8.5 ()
[2020-10-07 14:00:08.498] [INFO] console - SSL -- enabled
[2020-10-07 14:00:08.499] [INFO] console - SSL -- server key file: /etc/ssl/uni/uni.edu.cn_server.key
[2020-10-07 14:00:08.502] [INFO] console - SSL -- Certificate Authority's certificate file: /etc/ssl/uni/uni.edu.cn.crt
[2020-10-07 14:00:08.961] [INFO] console - You can access your Etherpad instance at
http://189.67.215.105:9001/
[2020-10-07 14:00:08.961] [INFO] console - The plugin admin page is at
http://189.67.215.105:9001/admin/plugins
[2020-10-07 14:00:08.961] [WARN] console - Etherpad is running in Development mode. This mode is slower for users and less secure than production mode. You should set the NODE_ENV environment variable to production by using: export NODE_ENV=production
[2020-10-07 14:00:11.814] [WARN] console - Update available:
Download the actual version 1.8.6
Can You help me one more time in order to get the etherpad plugin running ?
Must be due to invalid argument ... but how to find!
Thanks for help !
Best,
Svenja