Not all 2 for 1 coupons can be redeemed online, and in most circumstances can only be redeemed at Admissions when presenting the coupon and purchasing a full priced Adult ticket to get your second person in for free.
However, some 2 for 1 promotions are available to pre-book when following the instructions as advised on your coupon. For more information please check the terms and conditions on your coupon.