When testing out coupons with a live PayPal gateway we have the following things happening:
1. Discount is not applied to amount charged (user charged original, full amount)
2. Description sent to PayPal is not affected by using a coupon (prices in description: e.g. "X first month, X amount every month after" do not change)
Allow free signup is unchecked and free trial period is set to disabled.
Using latest ProSites (220.127.116.11) and WP (4.2.2).