when I try to enter this
https://steampowered.com/wallet I get this You don't have permission to access "/D/935/296433/000/origin.steampowered.com/wallet" on this server.
Sounds like some Steam internal problem. Try entering the code in the Steam client? Top "Games" menu -> "Redeem a Steam wallet code..."
Success!
You have added 14,91 to your Steam Wallet.
Working like a charm!