Beacons array is empty in didRangeBeaconsInRegion event in ionic ios app

I m using ionic native ibeacon library to detect beacons.I can detect beacons with android but when I try in ios ,i always see an empty beacon array. I tried these things ,but still cant see the beacons in ios (device is iphone 6s plus 11.4.1) (bluetooth service is enabled on device)

  • I tried both requestWhenInUseAuthorization and also requestAlwaysAuthorization.
  • I add NSLocationAlwaysUsageDescription and NSLocationWhenInUseUsageDescription key in info.plist

my code is like this, its working on android device

  import { Injectable } from '@angular/core';
    import { Platform, Events } from 'ionic-angular';
    import { IBeacon } from "@ionic-native/ibeacon";

    @Injectable()
    export class BeaconProvider {
      delegate: any;
      region: any;
      constructor(
        public platform: Platform,
        public events: Events,
        private iBeacon: IBeacon
      ) {
         this.initialise(); 
      }

      initialise(): any {
        let promise = new Promise((resolve, reject) => {
          if (this.platform.is("cordova")) {
            this.iBeacon.requestAlwaysAuthorization(); 
           // ALSO try this one too this.iBeacon.requestWhenInUseAuthorization();
            this.delegate = this.iBeacon.Delegate();
            this.delegate.didRangeBeaconsInRegion().subscribe(
              data => {
                this.events.publish("didRangeBeaconsInRegion", data);
               //console.log("didRangebeacons__" + JSON.stringify(data)); // empty beacons array
              },
              error => console.error()
            );
            this.region = this.iBeacon.BeaconRegion("deskBeacon", "e2c56db5-dffb-48d2-b060-d0f5a71096e0");
            this.iBeacon
              .startRangingBeaconsInRegion(this.region)
              .then(
                () => {
                  resolve(true);
                },
                error => {
                  console.error("Failed to begin monitoring: ", error);
                  resolve(false);
                }
              );
          } else {
            resolve(false);
          }
        });

        return promise;
      }
    }