Go to http://www.SonyEntertainmentNetwork.com
Click "Manage Account" and sign in with your Sign-In ID(E-mail Address) and Password.
Click on "Redeem Prepaid Card".
Enter the code printed on the voucher or PlayStation Network Card and click "Continue".
If the code is valid, you will be presented with a description of what the code will deliver to your account. Press the "Redeem..." button to add the item or funds to your account.
The game will now be available for download in "my library" on your ps4
After downloading go to your account and restore licenses if not you will keep receiving an error message