Welcome to Flyertalk and welcome to the BA forum.

I doubt we can find out much more given the information so far provided. There could be a number of causes, for instance BAEC tried to get the cash from your card and your card company declined payment. Or BAEC may have suspected there is something wrong with your account or your transaction. Your best bet, as the purchaser of the ticket, is to call BAEC and find out as precisely as you can what has happened and why. We can then advise further in terms of solutions. Don't be bounced into a decision if one comes up - there are certain remedies where (e.g.) accepting a refund turns you into a former customer.