Saving file to Downloads directory using Ionic 3

the problem was lack of permission. Here is the working code that can download file to downloads directory:

async downloadFile() {
  await this.fileTransfer.download("https://cdn.pixabay.com/photo/2017/01/06/23/21/soap-bubble-1959327_960_720.jpg", this.file.externalRootDirectory + 
  '/Download/' + "soap-bubble-1959327_960_720.jpg");
}

getPermission() {
  this.androidPermissions.hasPermission(this.androidPermissions.PERMISSION.READ_EXTERNAL_STORAGE)
    .then(status => {
      if (status.hasPermission) {
        this.downloadFile();
      } 
      else {
        this.androidPermissions.requestPermission(this.androidPermissions.PERMISSION.READ_EXTERNAL_STORAGE)
          .then(status => {
            if(status.hasPermission) {
              this.downloadFile();
            }
          });
      }
    });
}

To download the File to the Download directory you need to use Cordova File and FileTransfer Plugins.

import { File } from '@ionic-native/file';
import { FileTransfer } from '@ionic-native/file-transfer';

constructor(private transfer: FileTransfer) { }

fileTransfer: FileTransferObject = this.transfer.create();

//Use your File Url and name

downloadFile(file) {
  // Some Loading
  this.fileTransfer.download(url, this.file.externalRootDirectory + 
  '/Download/' + file).then(response => {
  console.log(response);
  this.dismissLoading();
  this.presentToast('File has been downloaded to the Downloads folder. View 
  it..')
  })
  .catch(err => {
    this.dismissLoading();
    console.log(err)
  });
}

Hope it helps.

import { File } from '@ionic-native/file';
import { FileTransfer } from '@ionic-native/file-transfer';
constructor(private file: File, private transfer: FileTransfer){}

let link = 'url_to_download_file';
let path = '';
let dir_name = 'Download'; // directory to download - you can also create new directory
let file_name = 'file.txt'; //any file name you like

const fileTransfer: FileTransferObject = this.transfer.create();
let result = this.file.createDir(this.file.externalRootDirectory, dir_name, true);
result.then((resp) => {
  path = resp.toURL();
  console.log(path);
  fileTransfer.download(link, path + file_name).then((entry) => {
    console.log('download complete: ' + entry.toURL());
  }, (error) => {
    console.log(error)
  });
}, (err) => {
  console.log('error on creating path : ' + err);
});