When you make a purchase, if you have a pre-existing iLok User ID, you will be asked to link it to your Gobbler account. Should you wish to review or change it, here's where to find it.
First, select "profile" in the upper-right "My Account" menu:
Once on your profile page, scroll down until you see "iLok Account Settings". Here, you can either unlink your account, or link/re-link it:
Make sure it's linked properly to the iLok User ID that you've used for your Marketplace Subscriptions.