hello, the coupon code and coupon discounts are displayed on all opc themes and they should get displayed also within the confirmation emails or elsewhere.
if you do not see them wihtin opc, you may want to alter the configuration here:
some options display plugin discounts, some show product discounts, some show coupon discounts without tax and some show coupon discount with tax. choose a proper display tapy which will show the desired value on your checkout.
best regards, stan