Just got an email from United for this and tried it out, worked smoothly. Coupon code was listed on the portal as eligible. I picked up two pairs of Ecco Windsor dress shoes (one laced, other slip-on), used the 20% off coupon and will pocket over 8000 miles with this purchase! Not bad for items that rarely go on sale and I needed them anyways, perfect timing.
(Make sure to use your United card for the extra miles)
(Make sure to use your United card for the extra miles)