Check your AmEx app most likely targeted.
Spend only at Dropbox to receive 40% credit each time up to $70 dollar, limited to the first 20,000 cards to save the offer.
Offer valid for subscriptions purchased in Australian Dollars at dropbox.com.
Not valid for subscriptions purchased via the Dropbox app.
Offer is limited to $70 per Card to which the offer is saved and only spend on this Card counts towards the Offer.
Excludes transactions where you do not spend directly with your Card to which the offer is saved, at Dropbox at www.dropbox.com. Offer valid at Australian website 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.
I used this offer last year (around December) but not targeted this time. Good one, if you are already paying for a dropbox account.