Debugging for https://www.reddit.com/r/node/comments/g1jkpz/getting_router_nodejs_error_beginner_please_help

server.js

const express = require('express');
const app = express();
const router = express.Router();

const makeMockHandler = (name) => (req, res) => {
    const message = `${name} --> ${req.originalUrl}`;
    console.log(message);
    res.json({ handler: name });
};

// Endpoint handlers, mock handlers since the issue is with route handler resolution
router.post('/', makeMockHandler('POST /'));
router.get('/', makeMockHandler('GET /'));
router.get('/:id', makeMockHandler('GET /:id'));
router.patch('/', makeMockHandler('PATCH /'));
router.delete('/', makeMockHandler('DELETE /'));
router.post('/login', makeMockHandler('POST /login'));

// Nest the endpoint handlers under a shared `users` api route
app.use('/api/users', router);

app.listen(80);