Getting access token returns 400

[josago97]

In the SpotifyHttp class, when the call is made to obtain the access token (line 31), the result is a 400 error (pasted below). Consequently, the other calls fail.

{"error":{"code":400,"message":"Unauthorized request","extra":{"_notes":"Usage of this endpoint is not permitted under the Spotify Developer Terms and Developer Policy, and applicable law"}}}