Your link shows instant discount, it should be adjusted and you should be able to pay discounted pricing.
While paying, check the price should become discounted for HDFC card. If you are doing no-cost EMI then the pricing will further reduce to adjust with the extra processing fees and any extra interest which occurs due to EMI. Try it once you will get the idea, just don't proceed to the OTP, otherwise the offer on the cc will get blocked.