REST api with odata failed

trying to call this rest api with POST  http://windchill25/WindchillRiskAndReliability13.1-REST/odata/Administration/CreateSessionToken

i’m getting

{
    "error": {
        "code": "FailedToAuthenticate",
        "message": "Login Authorization failed"
    }
}

In the Header i did add UserName, Password and GroupName.

This rest api work fine 
http://windchill25/WindchillRiskAndReliability13.1/dataengine.asmx/GetSessionToken

Any suggestion to debug this failure. (username and password are correct)