IonicNative File writeExistingFile not working?

in the succes response you have nativeUrl parameter this is the file location the you can use with the nativeUrl and FileOpener plugin to open this file
Example:

this.file.writeFile(cordova.file.externalDataDirectory,"Test.pdf","Hello World",true).then(succ=>{
    console.log("File write success : ", succ)

    this.fileOpener.open(
      succ.nativeURL,
      'application/pdf'//file mimeType
    ).then((success) => {
      console.log('success open file: ', success);
    }, (err) => {
      console.log('error open file', err);
    });
},
err=>{
  console.log(" write File error : ", err)
});