Update: Looks like it’s now dead.
R150 PlayStation Store Voucher – Free*
R150 Steam Voucher – Free*
*Use the coupon “UNL-150” at the checkout.
Easily add funds to your PlayStation Network wallet without the need for a credit card. Top up your PSN wallet to purchase full games, add-on content and more through PlayStation Store, accessible with your PS4, PS3 or PS Vita.
Note the coupon can only be used once on your account and has a limited amount of uses. So don’t expect it to last long.
Thanks to Lauren for the heads up.