Testing the Auspost API, I noticed a few things.

Label Settings

Each label needs to have it's own configuration for size, offset and branded option.
Offset and branded option so you can use pre printed labels.
size reference here - https://developers.auspost.com.au/apis/shipping-and-tracking/info/api-resources/labels

Create Label - https://developers.auspost.com.au/apis/shipping-and-tracking/reference/create-labels

{
                    "group": "Parcel Post",
                    "layout": "A4-1pp",
                    "branded": true,
                    "left_offset": 0,
                    "top_offset": 0
                },

Settings for domestic Shipping

https://developers.auspost.com.au/apis/shipping-and-tracking/reference/create-domestic-shipments

These need to be user selected for default settings.
authority_to_leave
allow_partial_delivery

"authority_to_leave":false,
"allow_partial_delivery":false,

International

Australia post does international also
https://developers.auspost.com.au/apis/shipping-and-tracking/reference/create-international-shipments

International Default settings

These need to be set as a default setting

classification_type
commercial_value
description_of_other

Shipment Validation

https://developers.auspost.com.au/apis/shipping-and-tracking/reference/validate-shipments

reference fields can be found here.
e.g classification_type fields are shown in there.