Sometimes happened to me to receive an alert about showing the credit card in the IB site; mainly when getting avios tickets for other people (what is a total pain if you are not traveling with them). After calling customer service a couple of times, the only option is to go to an Iberia counter at any time before the flight. As I travel almost every week, I usually go to the counter and show the credit card as soon as possible (mainly to avoid any credit card looses or cancellations). However, they have never asked my for the credit card if that alert at the time of booking didn’t appear.