InAppBrowser open an HTML file

Hey, I am making an app that is downloading a zipped file and then unzips in a folder (its a folder with an html file as well as some mobile js and CSS helper files). But I cannot seem to open the index.html file with the inAppBrowser. I have built a provider function that sends the file link back to page:

public openInApp(inApp){
    		return Observable.create(observer => {'user').then((user) => {
    				var inAppFolder = cordova.file.dataDirectory + 'files/' + user.user + '/' +;
    				var indexFile = '/' + inApp.syncFrom + '/' + inApp.indexFile;
    				var fileToOpen = inAppFolder + indexFile;
    				console.log("File to open: " + fileToOpen);


and then I try to open the html file like this:

  openInApp(inApp, key) {

      console.log("openInApp response: " + response);
      let browser = new InAppBrowser(response, '_system');

    }, error =>{
      this.presentToast("Error when opening inApp: " + error);

But I get that file is not found although it gets found in the provider. What am i missing? Is there another way to do this? Im trying to update a very old app that I have access to code and previously it was using iFrames. Is that better you think?

Any update on this
I am also looking for the solution if any solution let me know