Amazon Gift Card Not Working

I tried to use an Amazon.de gift card today in the morning and the system showed the error message “The gift card code you entered is invalid”. The code I entered was rejected as invalid even though the card was unused. I bought this Amazon.de gift card with a value of 50 € at a fuel station in Münster. I expected to be able to use the balance immediately, but the code does not work and I therefore cannot use the 50 € credit I paid for. I request that my Amazon.de gift card be activated so that the full 50 € balance becomes usable on my account as soon as possible.