getting org.springframework.messaging.converter.MessageConversionException in chat application

I’ve made simple real time chat application however when I run the application everything seems fine.
After the typing and sending the message , it is reflecting in the console tab but not reflected in chat application also getting exception as:
org.springframework.messaging.converter.MessageConversionException:
I am unable to solve this error. Please help.

<html xmlns:th="http://www.thymeleaf.org">
<head>
<meta charset="UTF-8">
<title>Real Time Chat Application</title>
<link
    href="https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css"
    rel="stylesheet"
    integrity="sha384-QWTKZyjpPEjISv5WaRU9OFeRpok6YctnYmDr5pNlyT2bRjXh0JMhjY6hW+ALEwIH"
    crossorigin="anonymous">
</head>
<body>
    <div class="container mt-4">
        <h1 class="text-center">Real-Time Chat Application</h1>
        <div id="chat" class="border rounded p-3 mb-3"
            style="height: 300px; overflow-y: auto;"></div>

        <div class="input-group mb-3">
            <input type="text" id="senderInput" class="form-control"
                placeholder="Your Name...">
        </div>

        <div class="input-group mb-3">
            <input type="text" id="messageInput" class="form-control"
                placeholder="Type Message...">
            <div id="input-group-append">
                <button id="sendMessage" class="btn btn-primary">Send</button>
            </div>
        </div>
    </div>
</body>
<script
    src="https://cdn.jsdelivr.net/npm/sockjs-client@1/dist/sockjs.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/stomp.js/2.3.3/stomp.min.js"></script>
<script>
    function setConnected(connected) {
        document.getElementById("sendMessage").disabled = !connected;
    }

    function connect() {
        let socket = new SockJS('/chat');
        stompClient = Stomp.over(socket);
        stompClient.connect({}, function(frame) {
            setConnected(true);
            stompClient.subscribe('topic/messages', function(message) {
                showMessage(JSON.parse(message.body));
            });
        });
    }
        
        function showMessage(message){
            let chat=document.getElementById('chat');
            let messageElement=document.createElement('div');
            messageElement.textContent=message.sender+':'+ message.content;
            messageElement.class="border-bottom mb-1";
            chat.scrollTop=chat.scrollHeight;
        }
        
        function sendMessage(){
            let sender=document.getElementById('senderInput').value;
            let content=document.getElementById('messageInput').value;
            let chatMessage={
                    sender:sender,
                    content:content
            }
            stompClient.send("/app/sendMessage",{},JSON.stringify(chatMessage));
            document.getElementById('messageInput').value='';
        }
        
        document.getElementById('sendMessage').onclick=sendMessage;
        window.onload=connect;
</script>
</html>

//Controller class code
package com.chat.main.controller;

import org.springframework.messaging.handler.annotation.MessageMapping;
import org.springframework.messaging.handler.annotation.SendTo;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import com.chat.main.model.ChatMessage;


@Controller
public class ChatController {
    @MessageMapping("/sendMessage")
    @SendTo("/topic/messages")
    public ChatMessage sendMessage(ChatMessage message) {
        return message;
    }
    
    @GetMapping("/chat")
    public String chat() {
        return "chat";
    }
}

//Websocket configuration code
package com.chat.main.config;

import org.springframework.context.annotation.Configuration;
import org.springframework.messaging.simp.config.MessageBrokerRegistry;
import org.springframework.web.socket.config.annotation.EnableWebSocketMessageBroker;
import org.springframework.web.socket.config.annotation.StompEndpointRegistry;
import org.springframework.web.socket.config.annotation.WebSocketMessageBrokerConfigurer;

@Configuration
@EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer{

    @Override
    public void registerStompEndpoints(StompEndpointRegistry registry) {
        registry.addEndpoint("/chat")
        .setAllowedOrigins("http://localhost:8080")
        .withSockJS();
    }

    @Override
    public void configureMessageBroker(MessageBrokerRegistry registry) {
        registry.enableSimpleBroker("/topic");
        registry.setApplicationDestinationPrefixes("/app");
    }
    
}````
 [Exception][1] [1]: https://i.sstatic.net/TpsFv1dJ.png
  [Chat application][2][2]: https://i.sstatic.net/i4D42Dj8.png
[Controller] [3]: https://i.sstatic.net/cWFH5vlg.png
[Websocket Configuration][4][4]: https://i.sstatic.net/UzIro8ED.png