Once you've got it set up, the app should add the box to your account automatically, if it has no other users. If it has other users, it'll ask for a "pairing pin" which can be found from another user with access on their http://home.juice.net main page (look for the "users" icon/button that says "Guest Sharing Pin").

On web/PC, go to http://home.juice.net and log in. On the main screen, click the purple "+" button in the upper-right of the screen, then click "New JuiceNet Device". It should show your unit in the list of detected devices, so you click it there and it'll fill into the field. Then, click the "Add" button below, and you're done!

If it gives an error that it's already owned by someone else, you need the app to reset its ownership (it's not implemented in the web version). Add it in the app and at the screen asking for the PIN, tap "Reset Ownership" and follow the steps. At the end, after completing the plug/unplug cycle, it may hang. Simply exit and re-add it, it'll work.