Can't seem to send and get data correctly between javascript front end and python backend [duplicate]

The idea is I'm trying to send a set or list to the backend. I'm using JavaScript on the front end and sending the data via fetch. For the backend I'm using Flask.

const walls1 = new Set()

// Submit Button
document.addEventListener('DOMContentLoaded', function(){
    document.querySelector('#search_button').onclick = function(){
        // Send a GET request to the URL
        fetch('http://127.0.0.1:5000/search',{
            method:"POST",
            body: JSON.stringify(walls1),
            headers: {
                "Content-Type": "application/json" 
            }   
        })
        // Put response into json form
        .then(response => response.json())
        .then(data => {
            console.log(data)
            console.log(walls)
        })
    };
});

All I want to do is print this set in my backend for now, but can't seem do this successfully.

@app.route("/search", methods=["POST"])
def search():
    
  
    print(request.json) **// prints {}, but the set does have items, so this isn't right**
    print(request.data) **// b'{}'**
    info = {"success": True}
    return jsonify(info)

Update: It looks like the set I am sending from the front end to the backend is empty? But I don't understand why because console.log(walls) prints a non empty set