Deploy Progressive Web App error in Production

I add the PWA out of the jumspstart pro template.  However, it appears that the ActionView complaining about the manifest.json with the following error

 ActionView::Template::Error (Webpacker can't find application.css in /home/davidnghk/App6/fg/code/public/packs/manifest.json. Possible causes:
1. You want to set webpacker.yml value of compile to true for your environment
   unless you are using the `webpack -w` or the webpack-dev-server.
2. webpack has not yet re-run to reflect updates.
3. You have misconfigured Webpacker's config/webpacker.yml file.
4. Your webpack configuration is not creating a manifest.

Any ideas ?

Not sure what you're doing, but you might check that bin/webpack compiles everything correctly and spits out an application.css file.

You should have a spot below that, that says 

Your manifest contains: {#Should include text here}

Is that empty by chance? 

in case some one else hits this (I did) you need to make sure your RAILS_ENV=production when you compile the assets. config/webpacker.yml is set to only emit the css file in production environment, even though it seems to build the rest of the JS/CSS w/o it.

 there is already site.manifest in the app/public folder. You can use it.  json file is not necessary for pwas.