We created a custom Cartthrob plugin which applies a 10% discount to items in the cart if purchased before a certain date, which works fine.
But we also have a coupon code to give 10% off.
Coupons and discounts are "not to be used with with any other offer". It means if someone enters the coupon code, the our custom discount should not be applied.
I can't find any help on this and wondered if anyone has a suggestion/solution?