Welcome to the Auth0 Community, it’s great to have you here with us 
The audience value is not necessarily the domain. You will have created an API in Auth0, as part of that creation you would have specified an identifier value, the audience you specify in the getAccessTokenSilently() call is the identifier value you specified when you created the API in Auth0.
The following community post will also help you https://community.auth0.com/t/understanding-how-the-audience-concept-actually-works/34011
Please let me know if you have further questions.
Best regards.