Getting messages from the server.

SyncManager.java

@Override
protected void onResume() {
    super.onResume();

    SendBird.addConnectionHandler(YOUR_CONNECTION_HANDLER_ID, new SendBird.ConnectionHandler() {
        @Override
        public void onReconnectStarted() {
            SendBirdSyncManager.getInstance().pauseSync();
        }

        @Override
        public void onReconnectSucceeded() {
            SendBirdSyncManager.getInstance().resumeSync();
        }

        @Override
        public void onReconnectFailed() {
        }
    });
}