You can redeem your voucher code either in Account Management or at the checkout when you make a purchase.
You can reach Account Management in a number of ways:
Tap [PlayStation Store] on the home screen and go to [Online ID] > [Account Settings].
Go to PlayStation Store. Sign in, go to your Online ID at the top of the page and click [Account Settings].
Please check the voucher code troubleshooting articles for a solution.
A voucher code is a set of numbers and letters that can be used to top up your wallet, receive downloadable content, subscribe to a service or obtain discounts on purchases from PlayStation Store.
You can receive a voucher code on a top up card purchased in a store, with a game disc, in an email or from a website.