Your React client will run in development mode by default. When you want to deploy to a live server, you must build the front-end and serve the static files.
// build the client
cd client && npm run build
// serve the client
npm run serve
You can run this file before you deploy or set it as a post-build script in package.json if your hosting provider supports post-build scripts. Gravity includes the Herokupost-build script for you already.
Running The Client & Server Together
If you want to serve the static files in the same production environment as your server, you will need to add the following lines to server.js