onBackgroundData not called

Hello there,
I've an app

class KronosHBDFApp extends Application.AppBase {

    function initialize() {
        AppBase.initialize();
        uname=null;
        pwd=null;
        jsonloaded=false;
        dataj=null;
        timeDLJson=null;
        if(Sto.getValue("jsondata")==null){
		   	if(Toybox.System has :ServiceDelegate) {
	    		Background.registerForTemporalEvent(new Time.Duration(5 * 60));
	    	} else {
	    		Sys.println("****background not available on this device****");
	   		} 
	   		
	   		Background.registerForOAuthResponseEvent();
		}   		
        
    }
    
    (:background)
    function onBackgroundData(data) {
    	Sys.println("obg ");
	}
	
	function getServiceDelegate(){
    	Sys.println("getServiceDelegate ");
    	return [new JsonBackground()];
    }
}

(:background)
class JsonBackground extends Toybox.System.ServiceDelegate {
	var realtoken;
	
	
	function initialize() {
		Sys.ServiceDelegate.initialize();
		realtoken=null;
		
	}
	
	/***********/
	function handleAccessResponseJsonHB(responseCode, data) {
    	Sys.println("handleAccessResponseJsonHB");

        // If we got data back then we were successful. Otherwise
        // pass the error onto the delegate
        if( data != null) {
        	Sys.println("data handleAccessResponseJsonHB OK "+data);  
        } else {
            Sys.println("Error in handleAccessResponseJsonHB "+responseCode + " " + data);
        }
        var ret=null;
        if(Sto.getValue("token")==null){
        	ret={"token"=>realtoken,"jsondata"=>data};
        	Sys.println("case1");
        }else{
        	ret={"token"=>Sto.getValue("token"),"jsondata"=>data};
        	Sys.println("case2");
        }
        Sys.println(ret);
        Bg.exit(ret);
        
    }
}    

class KronosHBDFView extends WatchUi.DataField {

    function onUpdate(dc) {
        Sys.println("onupdate");
    }
}