How to redeem Facbeook Game Gift Cards
1. Go to the redemption page (https://www.facebook.com/giftcards) and tap Redeem Code.
2. Enter the PIN code found on the back of your card and tap Redeem.
3. Select your preferred currency and tap Continue.
The entire value of the card will be added to your account balance, which you can then use to purchase items for games. Keep in mind you won't be able to use the card again once you redeem it.
Facebook Game Cards are only redeemable for Facebook games and can't be used for advertising.
Any further additional assistance can be acquired by contacting Facebook support at the following link : https://www.facebook.com/help/contact/146600035918755