MQTT Client cross-account to connect and publish to AWS IoT MQTT Broker

I need to use MQTT Client (ca, crt, key) from Lambda in Account A to connect to the AWS IoT core MQTT broker in Account B through mqtt publish. Here's what I've tried so far but it hasn't worked. Lambda is configured with NodeJS Node.js 20.x. Am I missing something?

const mqtt = require('mqtt');
export const handler = async (event) => {
        const mqttEndpoint = 'xxxxxxxx-ats.iot.us-east-1.amazonaws.com';
        const clientId = 'ThirdParty_xxxxxx_Cloud';
        const topic = 'xxxx/xxxx/xxxx/xxxx/xxxx';

        // Load SSL certificates and private key
        const fs = require('fs');
        const ca = fs.readFileSync('./AmazonRootCA1.pem');
        const cert = fs.readFileSync('./certificate.pem.crt');
        const key = fs.readFileSync('./private.pem.key');

        // Connect to MQTT broker
        const mqttClient = mqtt.connect(mqttEndpoint, {
            protocol: 'mqtts',
            port: 8883,
            clientId: clientId,
            ca: ca,
            cert: cert,
            key: key,
            rejectUnauthorized: true, // Set to false if your broker uses self-signed certificate
        });

        // Handle incoming messages
        mqttClient.on('message', (topic, message) => {
            console.log(`Received message on topic ${topic}: ${message.toString()}`);
            // Handle the message as needed
        });

        // Publish a message
        const message = 'Hello from Lambda!';
        mqttClient.publish(topic, message);

        // Disconnect after a certain period or when done
        setTimeout(() => {
            mqttClient.end();
        }, 5000);
};