This the updating router part of the route ‘/parts’

// Update a part
router.put('/:id', async (req, res) => {
    try {
        console.log("data got",req.body);
        const [rows, fields] = await pool.query(
            'UPDATE partimages SET partname = ?, description = ?, company = ? WHERE id = ?',
            [   
                req.body.partname, req.body.description, req.body.company, req.params.id
            ]);

        res.json(rows);
    } catch (err) {
        console.error(err);
        res.status(500).send('Server Error');
    }
});

I am sending data from this function:

function UpdatePartfunc(formData, id) {
    fetch(`http://localhost:3000/parts/${id}`, {
        method: 'PUT',
        body: formData
    })
    .then(response => response.json());
}
var id = '6';

const formData = {
    id: '6',
    name: 'Test Part',
    description: 'This is a test part',
    company: 'Test Company',
};

UpdatePartfunc(formData, id);

I am trying to send the formdata from the frontend UpdatePartfunc to the API so that it can update the table data using the id.

Log of the API:

Listening at http://localhost:3000
data got: undefined
TypeError: Cannot read properties of undefined (reading 'partname')

Log of Frontend function:

PUT http://localhost:3000/parts/6 500 (Internal Server Error)
UpdatePartfunc @ try.js:2
(anonymous) @ App.jsx:14
VM9480:1 Uncaught (in promise) SyntaxError: Unexpected token 'S', "Server Error" is not valid JSON