401 Unauthorized: Error while retrieving Embed URL (embed power bi for customers-Python)

I took every steps in this [tutorial](https://docs.microsoft.com/en-us/power-bi/developer/embedded/embed-sample-for-customers?tabs=net-core) and got all the required [information / IDs / Parameters](https://docs.microsoft.com/en-us/power-bi/developer/embedded/embed-sample-for-customers?tabs=net-core#step-5---get-the-embedding-parameter-values). Also watched these [vids](https://youtube.com/playlist?list=PLib8Q64STW-tCZVSvBAuEIzBsVlf0C81f).

However, at the final stage when running the [sample python code (flask app)](https://docs.microsoft.com/en-us/power-bi/developer/embedded/embed-sample-for-customers?tabs=python#step-8---embed-your-content), and opening the localhost url in my browser I get this error:

```
Error Details:
401 Unauthorized: Error while retrieving Embed URL
Unauthorized:
RequestId: 0b143776-bc54-492e-80bc-5401ecf32fd3
```

Which I can't figure out why

it seems that I'm unable to get the token and 401 is return in `pbiembedservice.py` as the api response (last line):
```
class PbiEmbedService:

def get_embed_params_for_single_report(self, workspace_id, report_id, additional_dataset_id=None):
'''Get embed params for a report and a workspace

Args:
workspace_id (str): Workspace Id
report_id (str): Report Id
additional_dataset_id (str, optional): Dataset Id different than the one bound to the report. Defaults to None.

Returns:
EmbedConfig: Embed token and Embed URL
'''

report_url = f'https://api.powerbi.com/v1.0/myorg/groups/{workspace_id}/reports/{report_id}'
api_response = requests.get(report_url, headers=self.get_request_header())
```

Other posts were not very helpful, can someone help me with that