The British apparently misuse the term ‘rain check’ (or cheque as they spell it) as a synonym for refund.
As originated in baseball, it’s a voucher issued to ticket holders for a rained-out game, allowing them to attend on a makeup date. You don’t get your money back. More broadly, it’s a slip given out by a store when they run out of stock that allows you to buy something later at the sale price.
They never quite got this distinction over there. Then again, you have to be careful about throwing around the word “misuse”. A good resource is the blog Separated By a Common Language, which delves into usage differences between US and UK English, without getting all tut-tutty about it.