How to display the label on google maps

Ionic Framework ionic-v3
1

I am trying to display the coordinates on google map but I can not make the label appear on the map to see all the location

<agm-map [latitude]="lat"[longitude]="lng" [zoom]="15"
      [zoomControl]="false">
  <agm-marker *ngFor="let location of tracks" [latitude]="tracks.lat" [longitude]="tracks.lng" [label]="tracks.label"></agm-marker>
</agm-map>


constructor(private geolocation: Geolocation) {
    this.lat=51.723858
    this.lng=7.895982

  this.tracks = [
            {lat:51.673858, lng: 7.815982,label: 'A'},
            {lat:51.373858, lng: 7.215982,label: 'B'},
        ];

  }