Flask 400 error?

@self.app.route("/getBalance", methods=["POST"])
        def _getBalance():
            return generate_response(json.dumps([all_users[request.form["id"]]["balance"], all_users[request.form["id"]]["bk"]]))

$.post("some url", {"id": uid}, function(data) {
        data = JSON.parse(data);
        balance = data;
        bal.innerText = "Баланс: " + balance[0];
        document.getElementsByClassName("cbalance")[0].innerText = data[1][0];
        document.getElementsByClassName("cbalance")[1].innerText = data[1][1];
        document.getElementsByClassName("cbalance")[2].innerText = data[1][2];
        document.getElementsByClassName("cbalance")[3].innerText = data[1][3];
      });