Sending you a microcharge is one of the ways we verify your funding card. We send the card a small charge (under £1.50) which is immediately refunded. It is the transaction reference which you will need to verify your card.
You will see a code C-XXXXXX on your bank statement. Once you enter this in-app, your card will be able to use with Curve.
Don't worry if you can't see the code straight away, sometimes it can take 3-5 days to appear on your statement. If you can't wait, you can phone your bank who will be able to give you the microcharge code.