A few days ago, this did not work for me - I would add the coupon, but then it would not reflect in the total. Today, I tried it again (website) and it worked okay. Guess they had a momentary store glitch.
What's more, this is 20% off of the original $15 price for ultimate - not the updated $17 price people are being charged per cycle. So, if you're on ultimate, it's a bit more of a savings.
Thanks! I’ll give it a go again. I’ll probably try to max out my subscription with this method as I’m sure the price will increase in the next three years