javascript express body has no contents

My problem is that req.body is returning ‘Object’. In the code below I get the TypeError message. The ‘req’ variable seems to contain nothing.

First, this is my curl testing command. I would like ‘here-again’ to show up in the file ‘/home/dave/test.txt’. I have tried putting ‘here-again’ in quotes.

curl -X PUT http://localhost:8008/config/ --data here-again

Below is my js code.

app.put('/config/',  function (req, res)  {
    const filename = '/home/dave/test.txt';
    const data = req.body;
    //res.send('body ' + data + ' ' + filename );
    console.log(data)
    fs.writeFile(filename, data, (err) => {
    if (err) {
        console.error(err);
        res.status(500).send('Error writing file');
    } else {
        res.send('Data saved successfully');
    }
  });
  // 
})

Below is my error message.

TypeError [ERR_INVALID_ARG_TYPE]: The “data” argument must be of type string or an instance of Buffer, TypedArray, or DataView. Received an instance of Object