Python Google Analytics Management API throws erro

I want to create an automated product data import for Google Analytics using the managament api (google analytics api v3) and python.

Now, I am facing the follwing issue: There was an API error : 403 : Forbidden

My oAuth works, because I can pull data from analytics. My account should also have sufficient user permissions, because I have created the same function with App Scripts and it worked (using the same property, account and customdatasourceId).

There must be something wrong with line 29 var daily_upload.

Did someone have similar experiences and hopefully a solution for that?

# -*- coding: utf-8 -*-
"""
Created on Mon Dec 18 11:06:45 2017

@author: brnccc
"""


from __future__ import print_function
import argparse
import sys

from googleapiclient.errors import HttpError
from googleapiclient import sample_tools
from oauth2client.client import AccessTokenRefreshError
from apiclient.http import MediaFileUpload


def main(argv):
    # Authenticate and construct service.
    service, flags = sample_tools.init(
    argv, 'analytics', 'v3', __doc__, __file__,
    scope='https://www.googleapis.com/auth/analytics')

    try:
        media = MediaFileUpload('ga_export.csv',
                          mimetype='application/octet-stream',
                          resumable=False)
        daily_upload = service.management().uploads().uploadData(
                accountId='XXXXXXX',
                webPropertyId='UA-XXXXXXX-X',
                customDataSourceId='XXXXXXXXXXXXXXXXXXX',
                media_body=media).execute()

    except TypeError as error:
      # Handle errors in constructing a query.
      print ('There was an error in constructing your query : %s' % error)

    except HttpError as error:
  # Handle API errors.
      print ('There was an API error : %s : %s' %
         (error.resp.status, error.resp.reason))

if __name__ == '__main__':
  main(sys.argv)

Edit: SOLVED Replaced oauth with service account authentication