Android pending intent not invoked in twilio incoming call -

i making calling app using twilio sdk have integrated stuff , in wokring condition. problem when android app remains in background long time app didn't receive incoming call request , pending intent not invoked twilio here code:

   if (!twilio.isinitialized()) {             /*          * needed setting/abandoning audio focus during call          */             twilio.initialize(context, new twilio.initlistener() {                  /*                  * sdk initialized can register using capability token.                  * capability token json web token (jwt) specifies how associated device                  * can interact twilio services.                  */                 @override                 public void oninitialized() {                     isinitialized = true;                     twilio.setloglevel(log.verbose);                     /*                      * retrieve capability token own web server                      */                     retrievecapabilitytoken();                 }                  @override                 public void onerror(exception e) {                     isinitialized = false;                     logging.e(tag, e.tostring());                     notifyonstoplistening(null,-1,context.getstring(r.string.error_message_not_connecting));                 }             });          } else {              retrievecapabilitytoken();         }   }  private void retrievecapabilitytoken() { // in success of api response      if (clientdevice == null) {             clientdevice = twilio.createdevice(capabilitytoken,devicelistener);         }          if(clientdevice != null) {                             intent intent = new intent(context, receivecallactivity.class);             intent.addflags(intent.flag_activity_single_top | intent.flag_activity_clear_top);             pendingintent pendingintent = pendingintent.getactivity(context, 0, intent, pendingintent.flag_update_current);             clientdevice.setincomingintent(pendingintent);             isintentadded = true;             logging.e(tag,"in addpendingintent intent added");         } } 

any suggestion , appreciated.