New Odoo user.

Trying to import outstanding invoices for customers as at take on date and balance this to GL.

Eventually found a spreadsheet by exporting one invoice.

In the first column of the spreadsheet it has the heading "Made Sequence Hole" and its value is TRUE.

Obviously, I do not want duplicated transactions in the GL as I have already imported the year-end balance sheet.

What is this?

Is there anywhere one can find more info or a video on how to do a take on from another system?