Although coupons have worked in the past - my last transaction did not process correctly.
I created a single use coupon for a specific user for site #548 Coupon: MOMELOCK
She renewed her subscription last night and used the coupon code. The log shows that she entered the valid code but it was not deducted from her payment. In the log it shows:
2015-05-27 1:49:39 am User added a valid coupon to their order on the checkout page: MOMELOCK
On the Coupon page - it does not show that the coupon was used.
I have granted access for you to check further.