Got an email saying the following, didn't see this posted anywhere.
The offer is valid from 00:00 (AEST) on 24 September 2019 until 23:59 (AEST) on 31 October 2019.
new or existing customer of amazon.com.au who has not previously signed in to the Amazon App (Australia store) and who has been invited by email from Amazon or who has viewed on site marketing whilst signed into their Amazon customer account, who will receive $10.00 off their first purchase of over $39 of “eligible items” made on the Amazon App (Australia Store)
Once the app is opened and signed in it should direct you to a page to claim the $10. I'm quite sure it mentioned you need to make the purchase in the app.
Feel free to edit if I got something wrong in this post.
I didn't get it…
So I'll spend my money at ebay instead…