All purchases in Australia include GST.
You may be able to claim GST back under the Tourist Refund Scheme TRS if you meet the conditions outlined on the following page:
https://www.abf.gov.au/entering-and-leaving-australia/tourist-refund-scheme/for-travellers
You are able to download a Tax Invoice by logging into your account on the Kogan.com website.
To download a copy of your Invoice, please see the following article: