Thanks for contacting us! Sorry about that, I have yet to put up a FAQ about dealing with that problem. We have found in the past to deal with problems like that you just add a N to the end of your post code, it signifies it as a blank space and accepts the payment. It has worked for all other countries so far, but this is new to us so please give us an email back to tell us whether or not it worked, we would really appreciate the feedback.
Usability experts would be turning in their graves... if only they were dead...