Authentication failure with oAuth/xAuth

I received a consumer key and a secret by mail and i'm trying to access more than provided as public.

I therefore want to authenticate with oAuth using the code from this repository:
https://github.com/musescore-com/python-api-wrapper/blob/master/connect…

but I failed to get withing the first request to obtain the temporary credentials with an excpetion of token reuqest denied.

I also tried using the xAuth authentication example and it fails with an error: "This OAuth consumer key is not xAuth enabled"

What needs to be further done in order to obtain premission to authenticate with oAuth/xAuth?