Hi,
Do you have exported your jar using “File > Export > Plugin Development > Deployable plug-ins and fragments” ?
The “File > Export > Java > JAR” doesn’t export a plugin that can be installed directly on Eclipse dropins folder.
I have updated the tutorial for this step.
https://github.com/eclipse/capella/wiki/Create-Addons#export-as-deployable-plugin
Regards
Philippe