You can pay an invoice by logging into the support center at http://www.ventureer.com/billing using your billing username and password. In the 'Billing' section click 'My Invoices' . If there is no credit card on file you wil l receive a message saying 'You do not currently have a credit card stored in the system. Click here to enter your credit card info.'
Ventureer currently only uses Paypal subscriptions so you will be automatically charged each month.