Heroku ERR! Missing script: “start”

After setting up a custom domain for our project and adding SSL certs, the next deployment started throwing this error:

npm ERR! Missing script: "start"

...

heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/" 

Checked out buildpacks and both were setup:

heroku buildpacks                                                   
=== Buildpack URLs
1. heroku/nodejs
2. heroku/ruby

And finally specify a node version on Heroku via my package.json:

  "engines": {
    "node": "14.x"
  },

Pushed again and voila, server was back up and running.