When dealing with OAuth 2.0 authorization one can run into all sorts of variations when it comes to the expected fields and grant types. This template represents the default scenario that today may not be used as often as in the past.
Here you will find the Client Credentials, Password Credentials and Authorization Code Grant Types, each with a different set of required fields.
Additionally at the bottom, just above the Use Custom Header box you will see a Get Access Token button left for the user.
The default fields that you will see belong to the Client Credentials grant type, but you still need to choose the desired Grant Type.
For Password Credentials you would have the following fields.
And for Authorization Code you would have these fields.