Hello Francirio16
Thank you for your query.
It’s just a guess, but I believe you might be entering the code in the wrong place. Make sure to select “voucher” among the payment methods, which will open a window where you can enter the 16-digit number and the CVC code. If my assumption is incorrect, please send us a screenshot to help us better understand what the issue might be:
Wishing you a nice evening, kind regards
ElenaG