Invoice To Be Paid By a Credit Card is an invoice which has in its terms of payment (TOP) a credit card (CC) and its number inserted in invoice form. Number is required.
The CC TOP and its number get autocompleted from a customer profile ('Finance' tab) or from a PNR, which becomes invoiced. Such invoices on transferring to finance are registered as paid and become balanced automatically.
There is an exception, when Credit Card (CC) should be treated as a cash. It refers only to 'eNett' CC type, which number starts with 553509.
In Company Settings → Settings → Invoicing: CreditcardToInvoiceAsCash any number can be set. If the customer' CC number starts with that one, then term of payment set in invoice is cash and CC number is not inserted.