How to fix bug in Promise?

Confluence Development Confluence Data Center
1

Hi,

I get error ClassNotFound for Promise:

private Promise<Response> sendPusherEvent(String channel, String event, String message) {
        long timestamp = System.currentTimeMillis() / 1000;
        String body = "{\"name\":\"" + event + "\", \"channel\":\"" + channel + "\", \"data\":\"" + message + "\"}";
        String signature = generateSignature(body, timestamp);
    
        String url = "https://" + cluster + ".pusher.com/apps/" + appId + "/events"
                + "?auth_key=" + key + "&auth_timestamp=" + timestamp + "&auth_version=1.0&auth_signature=" + signature;
    
        // Create and execute request correctly
        ResponsePromise requestBuilder = httpClient.newRequest(url, "application/json", body).post();
    
        // FIX: Convert ResponsePromise to Promise<Response>
        return requestBuilder;
    }

Also I can’t use 3rd API that working in Confluence 8. I just want to update my App to work in latest Confluence 9 Data Center.