Failure of OAuth2 with response code 503 via iPhone.

I have an app that uses makeOAuthRequest as the first step in downloading data from third party websites.

It works like clockwork using my Android phone on two third party sites.

It fails like clockwork using my iPhone on two third party sites.  Each time I get a call back after making the makeOAuthRequest call BUT the responseCode = 503.

Both sites are clearly not temporarily unavailable so I strongly suspect this to be an Apple <=> Garmin issue.

Have any other developers noticed this problem and is it being investigated by Garmin?

const REDIRECT_URI = "https://localhost/ciqauthcallback";  // provided by Final Surge

const RESPONSE_TYPE = "code";  // provided by Final Surge

function requestAuthorisation(){

        Comm.registerForOAuthMessages(mCallbacks.method(:requestAuthorisationResponseHandler));

        var params = {

                  "client-id"=>CLIENT_ID,

                  "redirect-uri"=>REDIRECT_URI,

                  "response-type"=>RESPONSE_TYPE,

        };

        Comm.makeOAuthRequest(

              AUTHORIZE_URI,

              params,

              REDIRECT_URI,

              Comm.OAUTH_RESULT_TYPE_URL,

              {

                     "code" => "code",

                     "error" => "error"

               }

       );

}