"Unknown word" error showing after adding postcss-loader

I kept getting "unknown word" error as well. It was a result that css cannot read comments with // but scss can... So I had to add the postcss-scss to the options after installing it with:

npm --save install postcss-scss

or (if you use Yarn)

yarn add --dev postcss-scss 

(webpack.config.js)

const WebpackNotifierPlugin = require('webpack-notifier');
const path = require('path');

module.exports = {
  module: {
    rules: [
      {
        test: /\.scss$/,
        loader: 'postcss-loader',
        options: {
          ident: 'postcss-scss',
          syntax: 'postcss-scss',
          plugins: () => [require('postcss-flexbugs-fixes')()]
        }
      }
    ]
  },
  plugins: [
    new WebpackNotifierPlugin({
      alwaysNotify: true,
      title: 'Enterprise',
      contentImage: path.join(__dirname, 'image.png')
    })
  ]
};

This might help someone, or me later again.

I got this error because instead of

@import '../../common.scss';

In my SCSS, I had mistakenly written

@import url('../../common.scss');

Removing the url() function got rid of the error.