I booked a few weeks ago, and the following code worked for me --

Go to the Gold Coast hotel reservations page. (Click on "STAY" at the top of the page).
Put in your Arrival & Departure date, etc.
Under "Offer/Group Code", type SALES23
(Leave the "Special Rate" box blank)
The answer will quote the discounted rate (along with the regular rate crossed out).

I think this is a generic discount rate offered by the GC Sales Department; good since 2023 until present time. For comparison, I typed in SALES24, and it also worked. Same discount.

Hope it works for everyone. It did for me.