Visit Apex Legends Syndicate Gold Gift Card Redeem, select "SIGN-IN" located at the top right and then select "CREATE AN ACCOUNT" to create an account first.
Step 2 :
After creating an account (make sure to verify after creating the account). Select "MY ACCOUNT"
Step 3 :
Select "Edit", enter your Apex Legends Mobile User ID in the "Player IDs" section then select "UPDATE".
Step 4 :
After completing the account and binding the Apex Legends account, you can proceed to redeem the code through the Apex Legends Syndicate Gold Redeem. Enter your voucher code, then select "REDEEM".