Rails / Heroku - No events being tracked

I have a Rails app deployed to Heroku, and I’m trying to get Sentry to track errors. I’ve already added the configuration to my application.rb file like:

Raven.configure do |config|
    config.dsn = 'MY DSN HERE'
end

I’ve installed the gem file, pushed to Heroku, and still no errors are being tracked. I’ve even tested offline outside of Heroku. Any suggestions?