Thanks Carole
I found the reference and filled in the order form and all the details about my credit card. When it asked me for my credit limit, I didn't bother to look at my last statement, but rounded the figure down to the nearest thousand. Unfortunately, I guess because I did not state the exact credit limit, my transaction was refused.
Now I have to get another credit card, or ask someone else to apply on my behalf.
Never mind, it will be only a short delay. As I said earlier, I learn something new every day.