Filepath not working in IOS

Hi, I am trying to upload file to server using filechooser for android and filepicker for ios.
For android everything is working fine. but for iOS i am getting error ‘Native: tried calling Filepath.resolveNativePath, but the FilePath plugin is not installed’
but the plugin is actually installed. i have installed 'ionic cordova plugin add cordova-plugin-filepath,
still getting same error.
Here is my code

chooseFileForIos() {
    this.filePicker
      .pickFile()
      .then(uri => {
        console.log(uri);
        this.toastService.presentToast('File Selected successfully');
        this.convertToBase64(uri, true)
      })
      .catch(err => console.log("Error", err));
  }

  chooseFileForAndroid() {
    this.fileChooser
      .open()
      .then(uri => {
        console.log(uri);
        this.toastService.presentToast('File Selected successfully');
        this.convertToBase64(uri, true)
      })
      .catch(e => {
        console.log(e);
      });
  }


  convertToBase64(imageUrl, isImage) {
    this.filePath
      .resolveNativePath(imageUrl)
      .then(filePath => {
        console.log(filePath);
        this.base64.encodeFile(filePath).then(
          (base64File: string) => {
            console.log("BASE 64 IS", filePath.split(".").pop());
            this.postData.ext = filePath.split(".").pop();
            this.postData.fileArray = base64File.split(",").pop();
            if (isImage == false) {
              this.fileArray.push({
                displayFile: filePath.split("/").pop(),
                base64File: base64File.split(",").pop() 
              });

Please tell me how to resolve path in iOS.