If your credit card is marked as inactive, there was an issue with a payment. The payment failed for some reason. Inactive means the card will be used for automatic payments anymore.
The card can be activated by doing a manual payment like adding balance to your account or ordering a manual renewal for example. Once this manual order was paid successfully be card will be used again for automatic payments.
You can also reactivate a card by removing it from the system and then adding it again.