How do I create a report of sales invoices according to the method of payment
The program does not know the method of payment of a sales invoice. It knows the bank or cash account where the receipt was posted. And it knows information about the receipt itself—date, reference if any, etc. If you want to record methods of payment (cash, cheque, PayPal, credit card, etc.) you would need to add a custom field. Then you could create a Sales Invoice Totals by Custom Field report.