I'm from Instamojo. You can't use a local URL. This is because a webhook request is a POST request that is made from our server. Therefore, the only URLs that we can make these requests to would be URLs that are publicly available. For testing purposes, I would recommend using...
Yes, it is possible to hide this line by using this app: https://www.instamojo.com/apps/details/com.instamojo.remove_branding/ (This link is only accessible when you're logged into your Instamojo account)...