The coupon and promotions documentation suggests that if you want to grant currencies via a coupon, to make a bundle that grants currency and grant that bundle via a coupon. We've implemented that, but have noticed that the RedeemCouponResult doesn't include what currencies were granted as part of the bundle. I believe RedeemCoupon should return granted currencies, as that is after all part of the result.
This feature has been requested before, so I'll link those posts here, but I'm reposting because the previous posts weren't in the Feature Requests section:
https://community.playfab.com/questions/5552/coupon-response-doesnt-include-currencies.html
https://community.playfab.com/questions/17544/redeemcoupon-timeout-and-grantedcurrency.html