The payment due in forty-five (45) days invoice is an invoice requesting that payment be sent specifically forty-five days after the invoice was delivered. Some individuals/companies like to provide a strict timeframe in which their clients/customers must pay for goods sold and/or services provided. This invoice is useful in notifying the client of an outstanding balance owed as well as providing a clear date upon which payment must be made. Depending on the collector and the situation, late payment fees may be charged to the client or the company may have other penalties in mind. There is a space at the bottom of the invoice that allows the sender to include a note explaining any possible ramifications of not making the payment on time.