Step 1:
Go to https://redeem.meplay.com/user to login (if you don't have an account, please register first).
Step 2:
Select "Add Player".
Step 3:
Select "+Add new player ID for a game".
Step 4:
Enter UID FIFA Mobile, then select "Add Player".
UID can be found in the game in the settings menu.
Step 5:
After add UID and verified, select "Redeem Code" or can go to https://redeem.meplay.com/game/fifa.
Step 6:
Choose an UID that has previously been verified, enter the voucher code then select "REDEEM"