When trying to request /api/v2/outbound/contactlists/{contactListId}/contacts/{contactId}, obviously contactListId and contactId are variables that holds the value of those, I got
The body of a 403 response generally indicates which permission is required, and GET /api/v2/outbound/contactlists/{contactListId}/contacts/{contactId} is documented as requiring outbound:contact:view. Please verify that the role assigned to the oauth client has appropriate permissions.