I used IE browser to key in the agoda specified hsbc link.
I used two different HSBC card, and found that ordinary gold card only has 5% discounts, while platinum card has 7%.
Furthermore, on credit card input page, after entering HSBC as the issuing bank, HSBC Card (7%) discounts is clearly displayed above Final price for Platinum card, while no such HSBC Card (7%) is displayed for Gold card, although the final price is actually already reflecting after discounts price.