Question

Since you do not have the coupon, we are
unable to give you the discount. (won't)​

Answer 1

since you do not have the coupon you won't be given the discount

Answer 2

Answer:

if you don't have coupon then we won't be able to give you the discount.

                                                         or

since you do not have the coupon then we won't be able to give you the discount.