Unable to refresh access token : response is "unauthorized_client"

I am getting an error when I try to refresh access token:

400 Bad Request

{error : "unauthorized_client"}

From the Google token URI:

{
  "error" : "invalid_request"
}

I read this answer here and the official Google documentation (which describes how a POST request should look) and I don't see any difference.

I captured my POST request (secrets removed):

POST /SHOWMERAWPOST HTTP/1.1
User-Agent: Google-HTTP-Java-Client/1.10.3-beta (gzip)
Pragma: no-cache
Host: requestb.in
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
Content-Length: 175
Connection: keep-alive
Cache-Control: no-cache
Accept-Encoding: gzip
Accept: text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2

grant_type=refresh_token&refresh_token=******&client_id=*******.apps.googleusercontent.com&client_secret=******

Java code which sends the request:

RefreshTokenRequest req = new RefreshTokenRequest(new NetHttpTransport(), new JacksonFactory(), new GenericUrl(
                    getSecrets().getDetails().getTokenUri()), REFRESH_TOKEN);

           req.set("client_id", getSecrets().getDetails().getClientId());
           req.set("client_secret", getSecrets().getDetails().getClientSecret());

           TokenResponse response = req.execute();

Is there anything wrong?

I created access and refresh token in OAuth2 playground and then i copied them to my app. It`s not allowed to have different clients for autorization and for token refresh.