The function (fileupLoad) is working fine with postman app, but not working from frontend as per requirement

Have a Query guys, please help me executing it!! I am not getting the desire result, The upload file function is not working as per requirement.The error block is executing instead of the actual function block.

main.component.ts:

  uploadFile() {
    console.log('Inside  uploadFile');
    const files: FileList = this.fileInput.nativeElement.files;
    console.log('Inside  uploadFile line 02');
    if (files.length === 0) {
      console.log('Inside  uploadFile 03');
      console.log('no file content here');
      console.log('Inside  uploadFile 04');
      return;
    };
    console.log('Inside  uploadFile 05');

    this.restservice.parseTable(files).subscribe((data: any) => {
      console.log('Inside  uploadFile 06');
      console.log('Data that i am sending: ' + data);
    },  (error) => {
      console.log('Inside  uploadFile 07');
      console.log('No Data Found' + error);
    });
}

Service.ts:

parseTable(files) {
    console.log('Inside parsetable function 01');
    const httpOptions = {
      headers: new HttpHeaders({
          'Content-Type': 'multipart/form-data',
      })
    };
    console.log('Inside parsetable function 02');
    const formData: FormData = new FormData();
    formData.append('file', files[0], files[0].name);
    console.log('Inside parsetable function 03');
    return this.http.post(this.backendAddress, formData, httpOptions);
  }

App.py:

@app.route('/uploader', methods = ['POST','GET'])
#@cross_origin(["http://localhost:4200"])
@cross_origin(allow_headers=['http://localhost:4200'])
def upload_file():
    print(request.files)
    # check if the post request has the file part
    if 'file' not in request.files:
        print('no file in request')
        return"no file in request"
    file = request.files['file']
    if file.filename == '':
        print('no selected file')
        return"no selected file"
    if file and allowed_file(file.filename):
        print("hello")
        filename = secure_filename(file.filename)
        #file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename))
        return "Successful"
    print("end")
    return"Bye"

OUTPUT:

Inside handleFileInput
Inside uploadFile
Inside uploadFile line 02
Inside uploadFile 05
Inside parsetable function 01
Inside parsetable function 02
Inside parsetable function 03
Inside uploadFile 07
No Data Found[object Object]