Mendeley API - unable to authorize using client credentials authorization flow

Question

I'm trying to authorize against the Mendeley API using the Client credentials authorization flow as described in the official documentation.

However, when I try:

curl -X POST -H "Content-Type: application/x-www-form-urlencoded" -u 799:1K2757WBBkLr9DOs -d "grant_type=client_credentials&scope=all" https://api.mendeley.com/oauth/token

I get this response:

{"message":"Credentials are required to access this resource."}

Trying out the other option:

curl -X POST -H "Content-Type: application/x-www-form-urlencoded" "https://api.mendeley.com/oauth/token?grant_type=client_credentials&scope=all&client_id=799&client_secret=1K2757WBBkLr9DOs"

makes no difference.