You can add a debit or credit card to your billing account if you want invoices to be paid automatically. To do so, log into your billing account and go to Billing » Payment Methods. Alternatively, you can go straight to billing.catalyst2.com/index.php?rp=/account/paymentmethods.

An image of the Payment Methods page. The page lists any existing debit or credit cards on your account. There is also an option to add a new card.
The Payment Methods page. You can use this page to add a debit or credit card, and you can remove any existing cards.

To add a new card, simply click the Add New Credit Card button and enter your card details. If you are adding more than one card then you can optionally add a description (to remind you what the card should be used for).

An image of the form used to add a new debit or credit card.
Adding a new card.