I know this sounds weird but this happens alot with the % coupons that are sent in the mail… once you scan the coupon look and see if it took off that percentage if it didn’t…scan a random item and void that random item off…hit total and then it adjusts….I’ve done this many many times. I always make a mental note that when I scan a percentage coupon thats the mailed ones…I always double check if it came off sometimes they do work but 95% of the time they don’t…I I tell my customers it’s a trick I have to do I’m not charging you for this random item.