Log into your account and then click on your name and click on "Payment Methods"

Click on "Add New Credit Card".

Fill out all of the credit card fields.

Credit card saved successfully.

Now you can use this card on your invoices.
Log into your account and then click on your name and click on "Payment Methods"

Click on "Add New Credit Card".

Fill out all of the credit card fields.

Credit card saved successfully.

Now you can use this card on your invoices.