I've followed instructions for setting up ServiceAPI:

http://world.episerver.com/documentation/Items/Episerver-Service-API/Configuration-and-overview/Setting-up-EPiServerServiceApi/

using (var client = new HttpClient())
{
  client.BaseAddress = new Uri("https://cmsservice.polarisdev.com");
  var fields = new Dictionary
  {
    { "grant_type", "password" },
    { "username", "admin" },
    { "password", "store" }
  };

var response = client.PostAsync("/episerverapi/token", new FormUrlEncodedContent(fields)).Result;

...

}

when running and hit the client.PostAsync(), the response is {"error":"invalid_grant"}

The IIS endpoint is localhost, self signed cert is in trusted store, host file is good, connection string is good (mapped to commerce database), confirmed the two EPiServerServiceApi recs are in the tblUserPermission in the CMS database.  

If anyone has seen this before and corrected the issue, please respond with fix.