The default Management API resides under “APIs” section, see below:
Note that Management API is a machine-to-machine application (also known as non-interactive application). This means, if you have authorised your application to consume Management API, then this will appear under “Machine to Machine Applications” tab, shown below:
Click on an authorised application, and from there, you will find the Client ID and Client Secret, shown below:
Alternatively, you can get the info from “Applications” tab (shown above), but make sure it is a machine-to-machine application and that it has been authorised by the Auth0 Management API.