Getting 503 error when SSE send subscribe request event second time

Question

Hi when am loading the page the first subscription request for SSE is working fine. but when SSE timeout and go for subscribe again am getting 503 error.

My backend code:

@RestController
@Slf4j
public class UpdateNotification {
    @Autowired
    SseService sseService;


    @GetMapping(value = "/api/v1/item/subscription", consumes = MediaType.ALL_VALUE, produces = MediaType.ALL_VALUE)
    public SseEmitter subscribe(@RequestParam("id") long id) throws  InterruptedException, IOException {
        SseEmitter emitter = new SseEmitter();
        sseService.add(id, emitter);
        emitter.onCompletion(() -> sseService.remove(id, emitter));
        emitter.onError((ex)->log.info("Error>> "+ ex.getMessage()));
        return emitter;
    }

    @Async
    public void produce(@RequestBody final MessageDTO message) {
        GetData(message);
    }

    public void GetData(final MessageDTO message) {
        sseService.getSsEmitters(message.getItemDTO().getId()).forEach((SseEmitter emitter) -> {
            try {
                emitter.send(message.getPrice(), MediaType.APPLICATION_JSON);
            } catch (IOException e) {
                emitter.complete();
                sseService.remove(message.getId(), emitter);
                e.printStackTrace();
            }
        });
    }
}

my frontend javascript code

function initialize() {
        var itemId=$("#itemId").text();
        const eventSource = new EventSource('/api/v1/item/subscription?id='+itemId);

        eventSource.onmessage = e => {
            const msg = e.data;
            $("#price").text(msg);
            Notification.requestPermission(function () {
                if (Notification.permission === 'granted') {
                    // user approved.
                    var text = msg;
                    var notification = new Notification('Notification Alert!', {body: text});
                    setTimeout(notification.close(), 6 * 1000) // close in 5 sec
                } else if (Notification.permission === 'denied') {
                    // user denied.
                } else { // Notification.permission === 'default'
                    // user didn’t make a decision.
                    // You can’t send notifications until they grant permission.
                }
            });
        };
        eventSource.onopen = e => console.log('open');
        eventSource.onerror = e => {
            if (e.readyState == EventSource.CLOSED) {
                console.log('close');
            } else {
                console.log(e);
            }
        };
        eventSource.addEventListener('second', function (e) {
            console.log('second', e.data);
        }, false);
    }

    window.onload = initialize();

first request send request successfully

When timeout happen subscription request automatic generate which throwing 503 error

I have no idea why am getting 503 on subscribe again after timeout. Please help me to solve this problem.