I got Cannot GET / for backend deployment

I’m trying to deploy MERN stack project. I could deploy my client side, but I kept getting Cannot GET / for server side.
it said Build successful :tada: but when I check browser, it says Cannot GET /.
My package.json is like below.

 "scripts": {
    "start": "nodemon index.js"
  }

And Build Command is npm install, start command is nodemon index.js

This feels like it’s related to your other post: https://community.render.com/t/how-to-set-build-command-and-publish-directory-for-mern-stack-project/8842

Alan