It’s likely to be one of two things. The first, that you may not have reached the £40 minimum spend just yet.
The second reason could be that your card may be due to expire on the day your delivery is due. We only take payment for orders once they’ve been delivered, not when you place an order. Unfortunately, we can’t verify your new card as it can’t be activated until your current one expires.
If you don’t think it’s either of the above, you’ll need to contact your bank to ensure there are no problems with your card. They’ll also be able to verify a new card for you.