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

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