Camera preview issue not set on send to back

I setup the camera like the docs but it does not display on send to back despite when i refresh it loads the camera full window size and then disappears from page again. What should i do? anybody can help me out on this please.

import { Component, AfterViewInit, ElementRef, ViewChild } from '@angular/core';
import { NavController, Platform } from 'ionic-angular';
import { CameraPreview, CameraPreviewPictureOptions, CameraPreviewOptions, CameraPreviewDimensions } from '@ionic-native/camera-preview';
@Component({
  selector: 'page-home',
  templateUrl: 'home.html'
})
export class HomePage implements AfterViewInit {
  pictureOpts: any;

    
  picture: string;
  @ViewChild('canvas') objCanvas: ElementRef
  constructor(public navCtrl: NavController, private platform:Platform, private cameraPreview: CameraPreview) {

      
      const cameraPreviewOpts: CameraPreviewOptions = {
        x: 0,
        y: 0,
        width: window.innerWidth,
        height: window.innerHeight,
        camera: 'rear',
        tapPhoto: false,
        previewDrag: false,
        toBack: true,
        alpha: 1
      };
      
      // start camera
      this.cameraPreview.startCamera(cameraPreviewOpts).then(
        (res) => {
          console.log(res)
        },
        (err) => {
          console.log(err)
        });
    
      
    }
  
  ngAfterViewInit(){
   
  }
  onPlay() {
    console.log('play');
    const pictureOpts: CameraPreviewPictureOptions = {
      width: 1280,
      height: 1280,
      quality: 85
    }
    
    // take a picture
    this.cameraPreview.takePicture(this.pictureOpts).then((imageData) => {
      this.picture = 'data:image/jpeg;base64,' + imageData;
      console.log(this.picture)
    }, (err) => {
      console.log(err);
      this.picture = 'assets/img/test.jpg';
    });
}