Login to your Client Management Portal.

Navigate to the 'Billing' dropdown menu.

From the dropdown select 'Manage Credit Card'.

This will take you to a page where you can input your credit card details. 

Once you have entered your details click 'Save Changes'.

Inputting your card details allows the system to automatically settle invoices using the card details which you have entered. If you wish to disable automatic payments then remove the card details from your account.