youtube api 401 error youtubeSigupRequired

I am trying to upload a video to Youtube using Youtube API v3 and python and I got the following error.

An HTTP error 401 occurred:

{  "error": {   "errors": [    {"domain": "youtube.header","reason": "youtubeSignupRequired","message": "Unauthorized","locationType": "header","location": "Authorization"    }   ],   "code": 401,   "message": "Unauthorized"  } }

I have created my project, created my Key and Client AOuth 2.0 and google console and downloaded the client_secrets.json.

The code I run is the one provided by Youtube API sample_code to download (here) for python.

If for example I try to do a search using the corresponding sample code and my credentials it works perfectly and I don't know why it doesn't work when I want to upload a vide.

Could you please letting me know what I am doing wrong, please?

Thanks in advance