Clients expects an invoice generation after item fulfillment, but system will go with cash sale.
Reason: When a Credit Card is set as default on a Customer Record, it automatically populates the Payment Method upon creation of Sales Order. With that, a Cash Sale is expected to be created.
To create Invoices from Sales Orders, the options would be to use the Standard Sales Order – Invoice Form (or a Custom Form that does not have the Payment Method field), manually remove the Payment Method and Credit Card information before saving the Sales Order or unmark the Default checkbox for a Credit Card on the Customer Record.
Even though, the default credit card is removed from the customer record, when the customer make payment from the customer center role, by selecting a credit card by checking the fields; save this card & Make default, it automatically checks make default under the credit card section in the customer record. So, on the next sales order generation, again cash sales generate from SO on clicking bill button.