https://digitalapi.auspost.com.au/test/shipping/v1/prices/items
Headers:
Account-Number 03921213
{
  "from": {
    "suburb": "Sydney",
    "postcode": "2001",
    "country": "AU"
  },
  "to": {
    "suburb": "Ermington",
    "postcode": "2115",
    "country": "AU"
  },
  "items": [
    {
      "length": "20.0",
      "width": "20.0",
      "height": "30.0",
      "weight": "5.0",
      "features": {}
    }
  ]
}

https://digitalapi.auspost.com.au/test/shipping/v1/shipments
Headers:
Account-Number 03921213
{
  "shipments": [
    {
      "shipment_reference": "SC1031597727323",
      "customer_reference_1": "SC1031597727323",
      "email_tracking_enabled": true,
      "from": {
        "name": "Client name",
        "lines": [
          "82 Some Place"
        ],
        "suburb": "Brisbane",
        "state": "QLD",
        "postcode": "4000",
        "country": "AU"
      },
      "to": {
        "name": "Joe Smith",
        "phone": "123456789",
        "email": "joe.smith@reinteractive.com",
        "lines": [
          "123 Fake St"
        ],
        "suburb": "Sydney",
        "state": "NSW",
        "postcode": "2000",
        "country": "AU"
      },
      "items": [
        {
          "item_reference": "Some Product name",
          "product_id": "RET",
          "length": "20.0",
          "width": "20.0",
          "height": "30.0",
          "weight": "5.0",
          "packaging_type": "BAG"
        }
      ]
    }
  ]
}