The GCU $14.99 sign up was impossible on Sunday when I tried. A good hour of troubleshooting with no resolution. If someone is able to successfully sign up this week please post the steps you and the employee took to make this work.
The only viable way to even get the GCU membership to show at the POS was to print a $14.99 GCU from the preorder kiosk. Yet, once I did this, the system bounced the cashier out with an error message - making a checkout impossible.
Unless this is resolved (by someone posting that they renewed or signed up in the mean time with the steps to do so) it is likely impossible to sign up or renew Gamer's Club Unlocked at this time.