I tried your request to see where that takes in Postman and I get invalid_request.
This means that one or more of your parameters are invalid.
You should try to go to your applications and check again that the redirect URL is same as one you use in Postman for given application (or else you get invalid call), the client_id is same as in application and what kind of rights you are requesting are contained in the application.
A successful call should show in Postman the login page to your account.
PS: make sure that you don't have spaces inside the URL.
I actually never could get this to work in postman, no matter what I did, I took the same data and used the advanced rest client for chrome and all worked fine, just wanted to call that out. Could be just my postman, but had problems with this call for sure.
I also have the same issue.