How to charge credit card after Invoice already created?

We have a customer that pays their invoices in different ways depending on who did the purchasing.  Usually we mail them an invoice and they pay us.  However, on occasion they will request that we bill a credit card instead.  We already have the invoice created and are confused as to the proper procedure to pay an outstanding invoice with a credit card after the invoice has already been created in NetSuite. 

If we view the invoice, there is a yellow Accept Payment button we can click, and that takes us to a Payment screen where we can enter a Payment Method and actually enter credit card info.  However, each time we Save the transaction, we get an error message that the process failed because there was no e-mail address loaded (we use CyberSource, which apparently requires an e-mail address to process a CC transaction).  However, there is no place to enter an e-mail address at this point.