Seems to be targeted as only appeared on my AmEx Essential card.
OFFER TERMS
Valid online only. Excludes payments made in-person such as via PayPal Here.
Only valid for payments made in Australian Dollars, which will be shown by PayPal as "AUD".
When paying with a PayPal account, you must first link your Card here. You must also select your American Express Card at PayPal checkout.
Only Australian PayPal accounts are eligible for the offer, PayPal accounts created in all other countries are ineligible.
Offer is limited to $40 credit per registered Card. Only spend on the Card number you register counts towards the Offer.
Excludes transactions where you do not spend online or in-app using your registered Card through PayPal, such as payment made online at checkout without selecting “PayPal”.
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.
similar offer here: https://www.ozbargain.com.au/node/343362