Due to a higher than normal strain on the PSN from the influx of PlayStation 4 owners, the voucher code system has been shut down temporarily.
According to a post on the EU PSBlog;
We are aware that users are experiencing some disruption to the PSN service. To minimise the inconvenience we have suspended the “redeem voucher” functionality whilst we investigate further. Unfortunately this means that money cards, product vouchers, PlayStation Plus vouchers, PS3-PS4 upgrade vouchers and any other vouchers for digital content are not redeemable at this stage. Other PSN features such as log-in, online multi-player gaming, PlayStation Plus trial, PS Store (excluding voucher redemption), trophies, messages, friends etc. are all available.
We apologies and will provide an update to this announcement soon.
Note; this applies to the PSN when accessed from the PS3, PS4 or PSVita. It doesn’t apply to voucher redeeming system on the SEN website, so you could use that and your download list as a workaround if you’re crafty.
Update; users in the NA region are also reporting that they can’t redeem vouchers from their consoles – to the SEN with you, too!
We’ll keep you updated.