Here are the details from an email I just received:
This offer is valid for reservations of two nights or more booked between 21 August 2018 and 28 August 2018.
Sale ends at 23:59 AEST on 28 August 2018.
Bookings must be prepaid online at AccorHotels.com and this offer applies to all stays between 11 September 2018 and 10 October 2019 at participating hotels in Australia, New Zealand, Fiji and French Polynesia.
Note that bookings are non-cancellable & non-refundable.
You need to join their "Le Club", but this is free.
Don't forget to use your prefered cashback option too.
If you are staying in a more expensive hotel it is worth considering joining Accor Plus:
www.accorplus.com/en/australia
This will give you an extra 10% discount (which works out about 14% less than the non-Accorplus 30% off price).
You also get a free night stay (subject to avail) & 50% off most meals in most Accor places in Asia Pacific.
More comments & details about Accor Plus here:
www.ozbargain.com.au/node/366597
Can't understand why they always don't show Kangaroo Island Mercure in their sale! As if its not in Aus :o