Node.js Connector TypeError: res.status is not a function

Hallo

I am learning JS scripting and am making a RESTful API with the MariaDB Node.js Connector and Express.js.
But I am stuck on the above mentioned error it has to do with this line ".then((res) =>" because if I do this " .then(() =>" I get no error.
But I also don't get the "res.insertId" in the console.log. What I get is "User added with ID: undefined".
Thanks in advance.

Dimitris

app.post('/users', (req, res) => {
 pool.getConnection()
            .then(conn => {
            conn.query('INSERT INTO users values(?,?,?,?,?)', [ '', 123, 'testuser' ,'' ,'user'])
            .then((res) => {
                res.status(201).send(`User added with ID: ${res.insertId}`) //error on this line "TypeError: res.status is not a function"
                console.log(`User added with ID: ${res.insertId}`)
                conn.end()
                console.log('conn end')
            })
            .catch(err => {
                console.log(err)
                res.status(500).send()
                conn.end()
                console.log('conn end with error')
            })
        })
 })