@cpradio, thanks for your answer.
The instance is installed on the domain w|w|w.doc|u|ss.o|r|g (remove the pipes).
Here is the plugin list:
hooks:
after_code:
- exec:
cd: $home/plugins
cmd:
- git clone https://github.com/discourse/docker_manager.git
But I have to say I’ve installed the Discourse Spoiler Alert plugin earlier, then uninstalled it. I found no doc about uninstalling a plugin, so I simply removed it from the yml file then ran ./launcher rebuild app again.