Need an access database, for invoicing and recording payments. Have a Customer details, where an invoice is sent to, products with prices. invoice total calculated based on number of days for daily activity. So need to put in range of dates and it works out number of days then times it by the daily price for invoice total.
Payments received are entered and shown on the invoice as payment with a total carried forward for all invoices and payments.
Reports for individual customers for payment and invoice history.