Advanced API returns unauthorized_client when getting token using resource owner password credentials flow

[jameslin]

{
    'client_id': "xxxxxxx@company",
    'client_secret': "xxxxxxxxxx",
    'grant_type': 'client_credentials',
    # 'grant_type': 'password',
    'scope': "api",
    'username': 'xxxx',
    'password': 'xxxx',
}

This is the body I am sending, but I am getting `{'error': 'unauthorized_client'}` what am I missing?

Secondly, the documentation says the grant_type must set to `password`, but if I do that, I get `invalid_grant`