JavaScript fetch API and Python Flask header issue

I'm trying to POST a JSON payload to a Flask server running on localhost:8080.

Javascript

    fetch(SERVER_URL, {
        method: 'POST',
        mode: 'no-cors',
        headers: {
            'Accept': 'application/json',
            'Content-Type': 'application/json'
        },
        body: JSON.stringify({"hello": "world"})
    });

I'm using Python Flask for my server, and I just want to print the received JSON on the server side.

Python Flask

from flask import Flask
from flask import request

app = Flask(__name__)

@app.route('/route', methods = ['POST'])
def routeHandler():
    data = request.get_json()
    print(data)
    return 'got it'

app.run(port = 8080)

The print statement is triggered, but data is None. After reading the Flask API documentation, I know that one of the reasons why data could be None is when the correct content type is not set on the request. To check this, I made the following change

 data = request.get_json(force = True)

which bypasses the is_json() check and continues parsing. This worked, suggesting there's something wrong with my headers. However, I have ensured that my fetch request is consistent with the API documentation so I'm not sure where I'm going wrong.

I have sent the same request from Postman and it is successfully received on the server even without force = True. The only header generated in Postman is Content-Type: application/json.

Thanks for any assistance.