Download image not working on IOS device - React Native

I implemented functionality for download image in React Native using RNFetchBlob Its Working fine with android but on IOS device it's not working.

Following is my react native code for download functionality.

downloadImg = (url) => {
      var that = this;
      async function requestCameraPermission() {
        const granted = await PermissionsAndroid.request(
          PermissionsAndroid.PERMISSIONS.WRITE_EXTERNAL_STORAGE,
          {
            title: 'Test App',
            message: 'Test App needs access to your gallery ',
          }
        );
        if (granted === PermissionsAndroid.RESULTS.GRANTED) {
          that.actualDownload(url);
        } else {
          Alert.alert('Permission Denied!', 'You need to give storage permission to download the file');
        }
      }
      if (Platform.OS === 'android') { 
        requestCameraPermission();
      } else {
        this.actualDownload(url);
      }
}


actualDownload = (url) => {
          var date = new Date();
          var image_URL = url;
          var ext = this.getExtention(image_URL);
          ext = "." + ext[0];
          const { config, fs } = RNFetchBlob;
          let PictureDir = Platform.OS === 'ios' ? fs.dirs.DocumentDir : fs.dirs.PictureDir;
          let options = {
          fileCache: true,
          addAndroidDownloads: {
              useDownloadManager: true,
              notification: true,  
              path: PictureDir + "/Images/image_" + Math.floor(date.getTime()
              + date.getSeconds() / 2) + ext,
              description: 'Image'
          }
          }
          config(options).fetch('GET', image_URL).then((res) => {
              console.log("Thank you","Image Downloaded Successfully."); 
          });
    }