Trouble deploying node js API to heroku. How to set up correctly?

Question

PostgreSQL

I'm new to express js
. I'm trying to deploy my project to Heroku
. But due to incorrect database settings, requests get 503

index.js errors.

require('dotenv').config()
const express = require('express')
const sequelize = require('./db')
const models = require('./models/models')
const cors = require('cors')
const fileUpload = require('express-fileupload')
const router = require('./routes/index')
const errorHandler = require('./middleware/ErrorHandlingMiddleware')
const path = require('path')

const PORT = process.env.PORT || 80

const app = express()

app.get('/', (req, res) => {
  res.end('<h1>Home</h1>')
})

app.use(cors())
app.use(express.json())
app.use(express.static(path.resolve(__dirname, 'static')))
app.use(fileUpload({}))
app.use('/api', router)


// Обработка ошибок, последний middleware
app.use(errorHandler)

const start = async () => {
  try {
    await sequelize.authenticate()
    await sequelize.sync()
    app.listen(PORT, () => console.log(`Server started on port ${PORT}`))
  } catch(e) {
    console.log(e)
  }
}
start()

db.js

const {Sequelize} = require('sequelize')

module.exports = new Sequelize(
  process.env.DB_NAME,
  process.env.DB_USER,
  process.env.DB_PASSWORD,
  {
    dialect: 'postgres',
    host: process.env.DB_HOST,
    port: process.env.DB_PORT
  }
)

In the .env file, the variable DB_HOST = localhost
I think the problem is somewhere here

. more than a year ago I tried to deploy the application on ROR and in the config on the Heroku website I had to specify the database URL and the secret key
Where to get all this, I can’t remember anymore and find at least some information about it

somewhere