I was able to resolce this issue by subscriting to the webhook API settings in sandbox. ALso we should not be using localhost URL. Instead we need to use ngrok and use https url. 

I was able to create a handler and provide that handler in webhook notification and am able to get the response now. 

Problem now is, how to validate uniqueness of the transaction. FOr exmaple if we create 10 transactions, I get webhook response in indeterministic time. In such cases how to map which response form web hook should be associated with whom.