So I've been tweeting HSBC all month to provide me with the updated code. They couldn't figure it out. Seems Expedia updated their form overnight and hence I've found the code despite HSBC still having the old one of their website. Tested and it worked for me.
Enjoy 10% off* select hotels on Expedia.com.au
HSBC and Expedia have teamed up to offer existing HSBC customers 10% off their hotel bookings on select hotels at expedia.com.au. All you need is any one of your HSBC cards.
Key points to remember when using your voucher code
Discount: 10% off the price of a single eligible hotel booking when booking with the “Pay online now” option. Not valid for use with the “Pay at the hotel later” option
Restrictions: Minimum stay of 1 night applies
Booking Dates: Valid for use by 23:59 on 30 September 2016. Limit of one coupon per person, per booking
Travel Dates: Until 31 December 2016
How to use your voucher
You must be signed in to your Expedia.com.au user account or registering as a 'guest' and making your booking using the “Pay online now” option, to take advantage of our discount offer
Simply visit http://www.expedia.com.au
Select the eligible Expedia Rate hotel you are interested in booking
During the booking process, on the payment page you will see the link "Enter a coupon or promotion code"
Select 'Enter a coupon code' and enter the voucher code in the relevant field
Click the "apply coupon" button. The applicable discount will be subtracted from the price of the travel reservation before the application of any taxes, applicable fees or additional costs.