I booked an Iberia flight BIO-MAD-BOS, economy class. I called Iberia and was told that there is charge for a check in bag. 85USD if prepaid online, and more if paid at the departure counter.

At Iberia.com "Manage your booking", these flights are shown as "Blue Class". There is a "I want more baggage" button under "Baggage in hold". Clicking that button got these error messages:

"Sorry, your session is in an invalid state ..."
"We are not able to compute the available services for this flight."

These flights are a month or so from now. Is it too early to prepay? Or is there a solution? Thanks.