Gmail add-on. Token Url

token_url.js

app.post('/token', (req, res) => {
    const { code } = req.body;
    console.log(code);
    const result = {};
    if (!code || code.length <= 0) {
        result.error = 'no valid code!'
    } else {
        result.expires_in = 2592000
    }
 
    res.status(200).send(JSON.stringify(result))
})