Just saw this in my offer inbox (Amex Platinum Edge)
Full Ts and Cs:
Payments must be made online at www.amazon.com.au/prime to be eligible for the offer.
Only payments for Amazon Prime monthly or annual memberships are eligible for the offer. All other payments at Amazon.com.au are ineligible.
Offer is limited to maximum of $30 credit per Card to which the offer is saved and only spend on this Card counts towards the Offer.
Offer is limited to the first 50,000 Cards that save the offer.
Offer end date is 18/12/2018.
Excludes transactions where you do not spend directly with your Card to which the offer is saved.
Offer valid at Australian website www.amazon.com.au/prime only.
Excludes transactions made through a third party establishment or payment processor.
Credit is not redeemable for cash or other payment form.
Credit should appear on your billing statement within 5 business days from qualifying spend but may take up to 90 days from the offer end date.
Credit will not be applied to your Card account if your Card has been suspended or cancelled.
Credit may be reversed if your qualifying purchase is refunded or cancelled.