Getting 404 when trying to make POST request from React frontend to Flask backend

I've been working on an app with a React.js frontend and a Python Flask backend (REST API), and one thing I want is for a form to send JSONified data from React to my Flask backend via a POST request, so that it can be processed.

However, I keep getting a 404 (not found) HTTP error, and it's really frustrating because I genuinely don't know how to debug this. I'm not sure what happens in between the request and why this is happening.

Here's the relevant React frontend code:

handleSubmit = (e) => {
        e.preventDefault();
        const text = {
            text : this.state.content
        };
        const sendText = {
            method: 'POST',
            headers: { 'Content-Type': 'application/json',
                        'Accept': 'application/json'
                    },
            body: JSON.stringify(text)
        };
        console.log(sendText.body);
        const url = 'https://cors-anywhere.herokuapp.com/http://localhost:5000/memes';
        fetch(url, sendText).then(response => response.json())
            .then(data => console.log(data));
        console.log("Success!") 

And here's the relevant Flask code

@app.route('/memes', methods=['POST'])
def memes():
    data = request.get_json()
    text = data["text"]
    return jsonify({"result": "success!", "text": text}), 200

Any idea what's wrong? Please feel free to ask any questions about what I'm doing or what I'm using.

Thanks in advance!