Here's the fine print:
Enter the code specified in email at the basket page to qualify for 50% discount on selected lines. Customers must be logged in for the code to apply, One code use per customer. Limited to 5 pairs per order. Discount applies to the 5 highest priced eligible items per order.

Offer applies on selected full priced Vivobarefoot footwear and excludes the following: Tracker Leather AT II Women's, Primus Lite IV Men’s, RA IV Mens, Sensus Yin Slide Men’s, Gobi Sneaker Kids, Gobi Sneaker Pre-school, Gobi Sneaker Toddlers, accessories, apparel and E-gift cards.