I took advantage of the 20% to refuel codes: 16 cards worth 80 63.84! Thanks to this promotion I can take my annual subscription to PS + 39.90 instead of 49.99 and Assassin's Creed Unity season pass for 23.94 instead of 29.99, a bargain.
However for anyone wishing to order more than 15 cards, Sony has introduced a restriction (error code E-82000156), the use of codes is then blocked for 24 hours.