Just noticed this on my offer on Qantas Ultimate Amex card, similar to this offer last year
Save the offer to your eligible Card and spend $400 or more, in one or more transactions, on Hotels or Car Hire online only at travel.americanexpress.com.au by 30/06/2022 to receive one $100 credit. Limited to the first 20,000 Cards to save the offer. Exclusions apply.
Got it on Explorer, not Platinum Charge. Both have unused travel credits on them fwiw.