I downloaded the plugin 2 weeks ago. I had quite a hard time getting the plugin to load initially, the fix was migrating the plugin to the database with the commands suggested from tomasp and dbarranco.
I then had to download a CA cert recommended by abjimenez and set the cert file to the environment, then run these commands.
bundle install --without development test postgresql sqlite --no-deployment
ruby bin/rake redmine:plugins RAILS_ENV=production
Your help is appreciated.