Service to Service Calls Using Client Credentials REST API call to generate token is throwing invalid Client Secrect always

Whenever iam tring to generate a token using https://login.windows.net/<tenant id>/oauth2/token REST call, iam always getting Client Secrect is invalid. I even tried generating a new client secrect still it says invalid.

Referred to this article: https://msdn.microsoft.com/en-us/library/azure/dn645543.aspx.