If the customer has paid you directly and you need to close the open invoice, you can pay using your reseller account balance.
On your reseller portal, locate the "Invoice" (ref 1.) in the “Customer Invoices” (ref 1.) tab and select it.
Click on the “Pay this invoice” (ref 4.) button on the top.
When asked to make the payment, select “Pay using reseller account balance” (ref 1.).
