I have installed the app "Markdown for Confluence". The key is
com.fulstech.confluence-markdown-app.
This was working the other day. Today I hit the / key - no app to be found. I can see it as installed. I am at a loss why this would suddenly disappear.
I also have a "Markdown Macros for Confluence" (key
com.atlassian.plugins.confluence.markdown.confluence-markdown-macro)
which does show up. I have tried to uninstall this in case it was causing a conflict, but can not do that either.