The "url" argument must be of type string. Received undefined

I am receiving this error during the deployment of my express/node app using App platform. Couldn’t figure what is the problem!

config.json:

{
  "development": {
    "username": "postgres",
    "password": "10300",
    "database": "weblogin",
    "host": "127.0.0.1",
    "dialect": "postgres",
    "logging": false
  },
  "test": {
    "username": "root",
    "password": null,
    "database": "database_test",
    "host": "127.0.0.1",
    "dialect": "mysql"
  },
  "production": {
    "use_env_variable": "DATABASE_URL"
  }
}