If you have an invoice with a Status of Pending or Partial Paid and a credit card saved on your account you will be able to make a manual payment.
Navigate to the Billing tab from the side menu. Select Invoice from the top horizontal menu bar.
Click the button Make a Payment.
Review your payment details in the pop up and click Submit.
It can take up to 15 min for the invoice table to update with the status of Paid.