I tried with adding the 20$ (1600 points) and didn't work. Probably because it's not a game as you mentioned.
I tried my luck by adding a with a 19.99$ or less game in the cart and didn't work either.
That confirm you can only buy games of 20$ or more. Thanks for your help!
The 5X10$ promo code offer was a bonus for pre-ordering SimCity Digital Deluxe. Current offer is 1X20$.
