User input not sent to server

My controls look like this

return (
        <div className='contentDiv'>
            <Container>
                <Form onSubmit={getFormData}>
                    <Form.Group className="mb-3" controlId="formBasicName">
                        <Row><Form.Control name="id" type="number" value={3} readOnly={ true }></Form.Control></Row>
                        <Row>
                            <Col>
                                <Form.Label>Forname:</Form.Label> <Form.Control name="firstname" type="text" placeholder="navn"></Form.Control>
                            </Col>
                            <Col>
                                <Form.Label>Efternavn:</Form.Label> <Form.Control name="lastname" type="text" placeholder="Efternavn"></Form.Control>
                            </Col>                           
                        </Row>                                                                      
                    </Form.Group>
                    <Row><Button type="submit">Create user</Button></Row>                    
                </Form>
            </Container>
        </div>
    )

And the function that is called on submit looks like this

const getFormData = async (event) => {              
        const data = new FormData(event.currentTarget);
        event.preventDefault();

        await fetch(`/api/newMember`, {
            method: 'POST',
            headers: { 
                "Content-Type": "application/json" 
            },
            body: JSON.stringify(data)
        })
        .then(res => {
            console.log(res);
        })
        .catch(err => {
            console.log(err)
        })        
    };

If I do this in the client (and fill the form with id=3, firsname=Lucky lastname=Luke):

for (let [key, value] of data.entries()) {
            console.log(key, value);
        }

I get (in the console)

id 3
firstname Lucky
lastname Luke

The server post method that does not receive the data from the client, looks like this

const express = require('express');
const knex = require('knex');
const cors = require('cors');
const bodyParser = require('body-parser');

const app = express();
const port = 3001;

    app.post('/api/newMember', (req, resp) => {
        const { id, firstname, lastname } = req.body;
    
        console.log(req.body);            
        
        const newMember = {
            id: id,
            firstname: firstname,
            lastname: lastname,       
        };        
    
        db('members').insert(newMember)
        .then(res => {
            resp.send(res)        
        })
        .catch(err => {
            console.log(err);
            return;
        })              
    })

app.listen(port, () => {
    console.log('Server listening on port: ' + port);
});

In the server, I have this code: console.log(req.body);. It jsut prints {}

Can anyone figure out what I’m doing wrong? Thanks