Have to tell them before you use coupon.

McDonalds just applies the coupon after the order process which makes it easy for drive thru use. Burger King does not do that. Dont forget to tell them at the intercom that you have the coupon. And then everyone in front of you better hurry up because you have 15 minutes to redeem.

CRXM about BURGER KING® App, v3.7.1