Your defenses (the NFTs you earn when opening packs) need to be LOCKED to be used in the game.
Step 1: After you have opened your Nightmare Packs, navigate to your inventory and select the Soulkeep tab to view your collection. Ensure that the filter is set to Owned.
Step 2: Click an individual card.
Step 3: Select an individual card to lock, or select all by clicking the white box located to the left of the drop-down filter menu (indicated by the leftmost red arrow).
Step 4: Click the Lock Cards icon (indicated by the rightmost red arrow above).
Step 5: View the popup, and determine whether these terms are acceptable to you. If so, input the number of days you wish to lock the card(s). 1 day is the minimum and 30 days is the maximum.
Step 6: Click Lock and and click ok within the resulting popup.
Step 8: View your newly locked card within your inventory.
Un-Locking Soulkeep Cards Individually
Step 1: Navigate to the Soulkeep tab of your inventory and identify and click the card you wish to unlock.
Step 2: Click the green lock icon next to the card you wish to unlock. Confirm that you would like to begin the unlocking process by clicking OK within the resulting popup.
Step 3: Note that the icon has shifted in color from green to orange - indicating that the unlocking process has begun.
Please Note: Cards must complete the full unlocking time specified in the original locking transaction.