(first post! woot)
This deal only applies to redcard members. Valid until November 1, 2019 and travel by December 31, 2019. The 5% RedCard discount cannot be applied to the promotion.
If you log into your redcard account you should see an ad for this promotion on the right side, and you will need to go through that link to use this coupon.
Select your hotel and dates and on checkout, there is a tab to expand to add promotion/coupon on the bottom right side.