ERROR: ChatConnector: receive - no security token sent.

[cext001]

I am trying to integrate my Dialogflow agent with Skype. I follow this link https://github.com/dialogflow/dialogflow-nodejs-client/tree/master/samples/skype to customize my bot responses. The webhook is deployed on Heroku. The issue is that I am getting this error "error: chatconnector: receive - no security token sent" always. The below CURL request looks fine

curl -X POST
https://login.microsoftonline.com/botframework.com/oauth2/v2.0/token
-H 'cache-control: no-cache'
-H 'content-type: application/x-www-form-urlencoded'
-H 'postman-token: 2774cb69-14bb-7247-d3bb-7bdda2de0e4c'
-d 'grant_type=client_credentials&client_id=f6f66a29-f184-48a0-9913-bda96c22be4f&client_secret=bkVCGV20*%25%2BfoicfITP333%40&scope=https%3A%2F%2Fapi.botframework.com%2F.default'

You can test this code and it clearly says there is no issue with Microsoft API regarding authentication. I am really stuck with this. Please help me in solving this.