Hi there Dependable9276,
It's vital that all your transactions be entered correctly so your books can be well balanced. QuickBooks Desktop is a great tool able to help you keep track of your invoices and payments so your customer balances are accurate. I can point you in the right direction for assistance with error messages.
The error message is designed to let you know that editing transactions that are in a previous period can affect your books. In order to know if you should be making this modification, or how else you should be proceeding to apply the payment to the invoice so that your books can be in order, I recommend reaching out to your accountant for guidance. They'll be able to specify how this payment should be accounted for since it affects a period in the past, as to make sure it's all represented correctly. if you'd like to find an accountant near you that has experience using QuickBooks, you can find one on our Find an Accountant site.
If you have any other questions, feel free to reach out here.
