Heroku does not Install Dev Dependencies
As workaround I have found: heroku config:set NPM_CONFIG_PRODUCTION=false which makes it possible to install dev dependencies. It's not a long term solution, because usually the server shouldn't be started in production with a babel or nodemon package, but at least it's possible to try it this way.
Ref: https://stackoverflow.com/questions/22954782/install-devdependencies-on-heroku
If anyone is running into this issue, just leave a quick comment here so that I know that this is still relevant.
I'm in the middle of deploying the api to heroku. Do you want a PR product ionizing the api under start and add a dev script you can do npm run dev for development. In development you should use nodemon.