Thank you all for your suggestion. I tried every single on but had no luck :-/ Maybe it is something special within the package itself ...

Hi folks, I may have a special challenge regarding the installation of packages via curl command in AEM 6.5 (on prem). There are many posts related to "how to curl", but none fitting to this problem.   We use this shell commands in a script for uploading - and in an later step - installing packages....