unauthorized_client error when geting access token from the refresh token

[lionwalker]

I added a client with password grant type and a user-related to it. when logged in with user credentials as follows.

curl -u MyClient:MySecret http://localhost/token -d 'grant_type=password&username=my_user&password=my_password'

then with the refresh token, I get from the above request I request an access token as follows.

curl -u MyClient:MySecret http://localhost/token -d 'grant_type=refresh_token&refresh_token=tGzv3JOkF0XG5Qx2TlKWIA'

but I keep getting an error unauthorized_client. how can I resolve this issue? how can I get access token from refresh token with password grant user?