If you purchased more than one voucher, each voucher must be redeemed individually. After you redeem the first voucher, you’ll be redirected to your shopping cart page. Simply, go back to the Redemption page to submit your second code so that it will also be added to your cart. If you only redeem one voucher, only one item will be shipped to you.
You can confirm that each voucher has been applied by looking for it under your sub-total (each voucher that you've redeemed will be listed there with the discount).