I was trying to book rail tickets in the UK over the internet with my credit card. The site asked for my "postcode". I put in my U.S. zip code and the site declined my purchase saying that my "postcode" did not match the one on record with my credit card. I tried a couple different credit cards and got the same result each time.
Is postcode something different than zip code? And, if so, where can I find my postcode as a quick internet search yielded nothing. Thanks!