For those who cant get it to work with paypal, try this.
apply the coupon on case mate website. discount will show. the click on paypal checkout. now if u try to apply coupon on paypal site, it will not work. just continue as usual and you will be redirected to case mate website for the final order confirmation. Discount will then appear once redirected.
I just used the coupon and got 2 jett cases, gray and blue. I will mix and match them on my phone.