Hi @Helvetios,
Welcome to the Auth0 Community!
Firstly, I recommend following our documentation on how to use the Management API in Actions below:
https://community.auth0.com/t/how-can-i-use-the-management-api-in-actions/64947
Additionally, it looks like you are taking this access token and trying to use it to make a POST request to your localhost. Unfortunately, it could not find your localhost URL and cannot send the POST request. Could you please confirm if you have a webserver configured locally, and listening at that port?
Thanks,
Rueben