/* src/app.js */

app.post('/numbers/multiply', (req, res) => {
  res.status(200).json({ result: multiply(req.body.a, req.body.b) });
});

Note we are using `app.post` rather than `app.get` to handle a POST request, and `req.body` rather than `req.params` or `req.query` to access the request body parameters.

There are also `app.patch`, `app.put` and `app.delete` methods to handle PATCH, PUT and DELETE requests respectively.