Heroku app showing blank page. react / express/ node - node.js

Question

https://peaceful-basin-17224.herokuapp.com/
Of course, "it works on my machine".
When I look at the network, I see the assets being loaded from index.html but nothing else.
Also, for some reason the npm run build doesn't seem to run. I'll heroku bash into the app and I won't find a /frontend/build
I've been messing with this since last night and feel like I haven't made any progress. Any help would be appreciated!
Part of my server.js
app.use(express.static(path.join(__dirname, '/frontend')));
app.get('/*', function (req, res) {
res.sendFile(path.join(__dirname, '/frontend/public', 'index.html'));
});
app.use(express.static(__dirname +'frontend'));
//Serve static assests if in production
if(process.env.NODE_ENV === 'production'){
//Set static folder
app.use(express.static('frontend/build'));
app.get('*', (req, res)=>{
res.sendFile(path.resolve(__dirname, 'frontend', 'public', 'index.html')) });
}
Here's my package.json:
{
"name": "backend",
"version": "1.0.0",
"description": "",
"proxy": "http://localhost:3001",
"main": "server.js",
"scripts": {
"test": "echo \"Error: no test specified\" && exit 1",
"start": "node server.js",
"server": "nodemon server.js",
"heroku-postbuild": "NPM_CONFIG_PRODUCTION=false npm install --prefix frontend && npm run build"
},
"author": "",
"license": "ISC",
"dependencies": {
"#mailchimp/mailchimp_marketing": "^3.0.69",
"express": "^4.17.1",
"simple-react-modal": "^0.5.1"
}
}

Answer 1

I think you can delete all of this code:
app.use(express.static(path.join(__dirname, '/frontend')));
app.get('/*', function (req, res) {
res.sendFile(path.join(__dirname, '/frontend/public', 'index.html'));
});
app.use(express.static(__dirname +'frontend'));
//Serve static assests if in production
if(process.env.NODE_ENV === 'production'){
//Set static folder
app.use(express.static('frontend/build'));
app.get('*', (req, res)=>{
res.sendFile(path.resolve(__dirname, 'frontend', 'public', 'index.html')) });
}
and put only this:
app.use(express.static(path.join(__dirname, './frontend/build')));
My react.js folder had the name "frontend" and it was at the same level with my server.js file, that's why it is one dot ./frontend/build. And don't remove build name and dont change it to any other name.
And please let me know if this answer helps.