Purchased UNC currency can be transferred into the game from the purchase page: https://worldwar3.com/unc.

First, items from Packs and Twitch Drops are stored in the web Inventory, which can be found on the following page: https://worldwar3.com/inventory.

From there, you can transfer the items into the game—simply select items you want to be transferred by clicking on them, and then confirm your choice by clicking the "Transfer" and then "Confirm transfer" buttons.