Passing JSON from Flask to Javascript returns empty. How can I let it show the dynamic value?

My app.route:

@app.route('/my_flask_route', methods=['POST'])
def receive_value():
    data = request.get_json()
    return jsonify(status="succes", data=data)

My JS:

document.addEventListener('DOMContentLoaded', function() {
    fetch('/my_flask_route', {
        method: 'POST',
        headers: {
            'Content-Type': 'application/json'
        },
        body: JSON.stringify({}),
    })
    .then((response) => {
    response.json().then((data) => {
    console.log(data)
    document.getElementById('input_value').value = data.my_dynamic_value;
    })
    .catch(error => console.error('Error fetching value:', error));
    })})

I can see in the developer console that the value I’m looking for is stored as JSON:

{
  "data": {
    "my_dynamic_value": 5.1
  },
  "status": "succes"
}

I just seem to be stuck at passing the value to the JS script to overwrite a spin box in my html. All I see as a result is:

[Log] {data: {}, status: "succes"}