Error: self-signed certificate When connecting to google FCM with XMPP protocol

Question

I am trying to connect to google Firebase Messaging with xmpp protocol with Node Js with node-xmpp-client But I am getting an TLS error

Below is the code:

const XMPP = require("node-xmpp-client");
config = {
  id: "push-notify-xmpp",
  key: "________KEY______",
  port: "5236",
  host: "fcm-xmpp.googleapis.com",
};
client = new XMPP.Client({
  jid: `${config.id}@fcm-xmpp.googleapis.com`,
  password: config.key,
  port: config.port,
  host: config.host,
  legacySSL: true,
  preferredSaslMechanism: "PLAIN",
});
client.connection.socket.on("error", function (error) {
  console.log("socket error");
  console.error(error);
  process.exit(1);
});

client.on("online", function (data) {
  console.log(
    "Connected as " +
      data.jid.local +
      "@" +
      data.jid.domain +
      "/" +
      data.jid.resource
  );
});

client.on("error", function (err) {
  console.log("server error");
  console.error(err);
  process.exit(1);
});

Error:

server error
Error: self-signed certificate
    at TLSSocket.onConnectSecure (node:_tls_wrap:1538:34)
    at TLSSocket.emit (node:events:513:28)
    at TLSSocket._finishInit (node:_tls_wrap:952:8)
    at ssl.onhandshakedone (node:_tls_wrap:733:12) {
  code: 'DEPTH_ZERO_SELF_SIGNED_CERT'
}

Also tried the command :

NODE_TLS_REJECT_UNAUTHORIZED='0' node appServer.js 

But above get an different error Unauthorised

Can Anyone have any Idea ow to deal with FCM server with XMPP