Python - Can't upload video to YouTube with service account: "youtubeSignupRequired"

I'm new to Google Cloud Platform and I'm trying to build a Python script that automatically uploads videos to YouTube. My goal is to run this script on a server, so I'm using a service account to avoid manual login prompts. However, I'm facing an "Unauthorized" error with the message "youtubeSignupRequired" during the upload process.

Here's a breakdown of the steps I've taken:

1. Created a Google Cloud project and enabled the YouTube Data API v3.
2. Created a service account. I was unable to find a "YouTube Content Manager" role, so I assigned the "Video Stitcher Admin" role, assuming it would grant the necessary permissions.
3. Downloaded the service account's JSON credentials file.
4. Installed the required Python libraries:google-api-python-client, google-auth-httplib2, google-auth-oauthlib.

My Python code for authentication and uploading is as follows:

import osimport google.authimport google_auth_oauthlib.flowimport googleapiclient.discoveryimport googleapiclient.errorsimport googleapiclient.httpimport jsonfrom jinja2 import Template# Scopes required to upload a videoSCOPES = ["https://www.googleapis.com/auth/youtube.upload"]def authenticate_youtube():    credentials = None    SERVICE_ACCOUNT_FILE = 'path/to/your/key.json'  # Replaced with the path to my JSON file    if os.path.exists(SERVICE_ACCOUNT_FILE):        credentials = google.oauth2.service_account.Credentials.from_service_account_file(            SERVICE_ACCOUNT_FILE,            scopes=SCOPES)    if not credentials:        print('Error: Could not find service account credentials.')        exit(1)    youtube = googleapiclient.discovery.build('youtube', 'v3', credentials=credentials)    return youtube# ... (rest of upload_video code) 

Despite these steps, I consistently encounter the following error when running the script:

googleapiclient.errors.ResumableUploadError: <HttpError 401 when requesting None returned "Unauthorized". Details: "[{'message': 'Unauthorized', 'domain': 'youtube.header', 'reason': 'youtubeSignupRequired', 'location': 'Authorization', 'locationType': 'header'}]">

I've verified the following:

• The YouTube Data API v3 is enabled in my project.
• The scopes in my code are correct for video uploads.
• The JSON credentials file is valid and in the correct location.
• My API usage quotas are not exceeded.

I'm unsure what else to check. Could someone please guide me? Is the "Video Stitcher Admin" role insufficient for this task? Have I missed a crucial configuration step in Google Cloud specific to using service accounts for YouTube uploads? Any assistance would be greatly appreciated!