Simply enter your Account Number and click "Pay Now." When you click on "Pay Now", you will be redirected to Paypal's secure website where you will first enter the amount to pay (under price per item). Then, you can pay with Paypal OR, if you do not have a Paypal account, you can simply pay with debit or credit card. If you do not have a Paypal account, look for the gray box which says, "Pay with Debit or Credit Card" (under Paypal's login boxes). There is no payment fee.
On your invoice, please find your Account Number (it is the same as your Patient ID)