Accounting Dilemma - Apply Amounts Received to Open Invoices

Tony2021 As an accountant myself, I would assume you have some sort of accounting system. If a customer does not supply the invoice numbers paid I would ask for a clarification or just apply the payment to the oldest invoices and leave whatever is left as a partial payment to the next oldest invoice. Most accounting systems will allow you to do so. I, thus, wonder why you want to try to do this is in Excel. It's quite meaningless! Suppose you have three open invoices, each $500 and you receive $1000 without any further information. Which two of these would you want Excel to pick as paid?