I am connecting to gateio websocket servers with the nodejs code below. Authentication works correctly when connecting to the futures.usertrades channel. But I am getting unexpected errors when connecting to the futures.login channel.

import ReconnectingWebSocket from 'reconnecting-websocket';
import IsomorphicWS from 'isomorphic-ws';
import CryptoJS from 'crypto-js';
import GateAPI from 'gate-api';

let client = new GateAPI.ApiClient();

let rws;

let initialize = () => {
    return new Promise((resolve) => {
        rws = new ReconnectingWebSocket(`wss://fx-ws.gateio.ws/v4/ws/usdt`, [], {
            WebSocket: IsomorphicWS,
            debug: false,
            maxReconnectionDelay: 10000,
            maxRetries: Number.POSITIVE_INFINITY,
            minReconnectionDelay: 5000,
            minUptime: 7500,
            connectionTimeout: 15000,
            startClosed: true,
        });

        rws.addEventListener('close', wsClose);
        rws.addEventListener('open', () => {
            wsOpen();
            return resolve(rws);
        });
        rws.reconnect();
    });
};

let pong = () => {
    return rws._ws.pong(function () {
        return null;
    });
};

let wsClose = () => {
    rws.reconnect();
};

let wsOpen = () => {
    if (rws._ws.on) {
        rws._ws.on('ping', pong);
    }
};

let data = {
    apiKey: 'xxx',
    apiSecret: 'yyy',
    userId: 11110001,
};

initialize(data).then((RWS) => {
    client.setApiKeySecret(data.apiKey, data.apiSecret);
    let spot = new GateAPI.SpotApi(client);
    let now = new Date().getTime();
    spot.getSystemTime().then((result) => {
        let processTime = new Date().getTime() - now;
        let serverTime = result.body.serverTime;

        RWS.addEventListener('message', (message) => {
            console.log(message.data);
        });

        let timeStamp = Math.ceil((serverTime + processTime) / 1000);
        let signatureString = `channel=futures.usertrades&event=subscribe&time=${timeStamp}`;
        let signature = CryptoJS.HmacSHA512(signatureString, data.apiSecret).toString(
            CryptoJS.enc.Hex
        );
        let auth = {
            method: 'api_key',
            KEY: data.apiKey,
            SIGN: signature,
        };

        rws.send(
            JSON.stringify({
                time: timeStamp,
                channel: 'futures.usertrades',
                event: 'subscribe',
                payload: [`${data.userId}`, '!all'],
                auth,
            })
        );

signatureString = `channel=futures.login&event=api&req_param=&time=${timeStamp}`;           
        signature = CryptoJS.HmacSHA512(signatureString, data.apiSecret).toString(CryptoJS.enc.Hex);
        let payload = {
            req_id: 'api_request_id_1',
            api_key: data.apiKey,
            headers: {
                Accept: 'application/json',
                'Content-Type': 'application/json',
                'Channel-ID': 'api_request_id_1',
            },
            signature: signature,
            timestamp: timeStamp.toString(),
            req_param: [],
        };

        let postData = JSON.stringify({
            time: `${timeStamp}`,
            id: 1,
            channel: 'futures.login',
            event: 'api',
            payload,
        });
   
        rws.send(postData);
    });
});

websocket futures.usertrades response;

{"time":1720051095,"time_ms":1720051095630,"conn_id":"61f6a33a935376da","trace_id":"2b3cf8924025c2d866e781c72775680c","channel":"futures.usertrades","event":"subscribe","payload":["11110001","!all"],"result":{"status":"success"}}

websocket futures.login response;

{"time":1720051095,"time_ms":1720051095632,"conn_id":"61f6a33a935376da","trace_id":"84ed781186f1da73ad60107c9e27386d","channel":"","event":"","error":{"code":1,"message":"request message need JSON scheme"},"result":{"status":"fail"}}

What am I missing or doing wrong. Thank you.