You need to either click on the url with the referral code or type it into your mobile browser when you sign up. There isn't a field that you type to code into. So if you want to use mine, click on the link below (preferably from your mobile device when you're ready to sign up)...

I used siklam's code.
My code is: http://get.shopkick.com/cupertino17823

Using it will get you 50 bonus shopkick points as a signup bonus. Thanks!